...

		location ~* ^.+.(ts)$ {
		    proxy_pass https://localhost:8445;
		    proxy_http_version  1.1;
		    proxy_set_header    Host $server_name:$server_port;
		    proxy_set_header    X-Forwarded-Host $http_host;
		    proxy_set_header    X-Forwarded-Proto $scheme;
		    proxy_set_header    X-Forwarded-For $remote_addr;
		    proxy_set_header    Upgrade $http_upgrade;
		    proxy_set_header    Connection "upgrade";
            proxy_cache proxy_cache;
            proxy_cache_key $host$uri$is_args$args;
            proxy_cache_valid 200 2m;
       	}

		location ~* ^.+.(m3u8)$ {
		    proxy_pass https://localhost:8445;
		    proxy_http_version  1.1;
		    proxy_set_header    Host $server_name:$server_port;
		    proxy_set_header    X-Forwarded-Host $http_host;
		    proxy_set_header    X-Forwarded-Proto $scheme;
		    proxy_set_header    X-Forwarded-For $remote_addr;
		    proxy_set_header    Upgrade $http_upgrade;
		    proxy_set_header    Connection "upgrade";
            proxy_cache off;
            expires -1;
       	}

Returning of static HTML pages on HLS port

Another way to workaround cross domain requests restrictions in browser is to return a static content, player page for example, on the same port that returns HLS content. To enable this feature, the following parameter should be set in flashphoner.properties file

hls_static_enabled=true

...

Passing a custom parameters when requesting a playlist

A custom parameters should be passed when requesting a playlist if reverse proxy authentication is set up:

hls_static_dir=client2/examples/demo/streaming/hls_static

...

https://wcs:8445/test/test.m3u8?key1=value1&key2=value2

The feature is supported since build 5.2.1959. The parameters passed will be returned in every playlist for every segment, this allows to authorize a viewer correctly on proxy server.

There will be an additional parameter sessionId in playlists, for example

hlsav_statictest_dir=/var/www/html/hls_static

If static content returning is enabled, browser will display the HLS player page by URL https://host:8445/hls-player.html. If this feature is disabled, server will return 404 Not found error by such URL.

Preloader for HLS stream playback

When first HLS subscribes connects to a stream on WCS server, especilally to CDN stream, it may take a time to split a stream to HLS segmets and to form a playlist. As a result, Safari browser on iOS devices may not be able to play HLS stream on the first attempt. To successfully play HLS stream in this case, the HLS preloader was added since build 5.2.371. The default preloader looks like this:

Image Removed

Since build 5.2.408 preloaders are divided by stream aspect ratio: 16:9, 4:3, 2:1

Default preloader segments are placed to /usr/local/FlashphonerWebCallserver/hls/.preloader folder when server is started

tree /usr/local/FlashphonerWebCallServer/hls/.preloader
/usr/local/FlashphonerWebCallServer/hls/.preloader
├── 16x9
│   ├── index0.ts
│   ├── index10.ts
│   ├── index11.ts
│   ├── index12.ts
│   ├── index13.ts
│   ├── index14.ts
│   ├── index15.ts
│   ├── index16.ts
│   ├── o/av_test_o.m3u8?sessionId=11&key1=value1&key2=value2

This is the internal WCS parameter to identify the subscriber for statistical purposes.

Returning of static HTML pages on HLS port

Another way to workaround cross domain requests restrictions in browser is to return a static content, player page for example, on the same port that returns HLS content. To enable this feature, the following parameter should be set in flashphoner.properties file

hls_static_enabled=true

The player page should be in directory defined by the following parameter

hls_static_dir=client2/examples/demo/streaming/hls_static

In this case (by default) the path to the player page files is set relative to WCS installation directory. A full path may also be set, for example

hls_static_dir=/var/www/html/hls_static

If static content returning is enabled, browser will display the HLS player page by URL https://host:8445/hls-player.html. If this feature is disabled, server will return 404 Not found error by such URL.

Preloader for HLS stream playback

When first HLS subscribes connects to a stream on WCS server, especilally to CDN stream, it may take a time to split a stream to HLS segmets and to form a playlist. As a result, Safari browser on iOS devices may not be able to play HLS stream on the first attempt. To successfully play HLS stream in this case, the HLS preloader was added since build 5.2.371. The default preloader looks like this:

Image Added

Since build 5.2.408 preloaders are divided by stream aspect ratio: 16:9, 4:3, 2:1

Default preloader segments are placed to /usr/local/FlashphonerWebCallserver/hls/.preloader folder when server is started

tree /usr/local/FlashphonerWebCallServer/hls/.preloader
/usr/local/FlashphonerWebCallServer/hls/.preloader
├── 16x9
│   ├── index0.ts
│   ├── index10.ts
│   ├── index11.ts
│   ├── index12.ts
│   ├── index13.ts
│   ├── index14.ts
│   ├── index15.ts
│   ├── index16.ts
│   ├── index17.ts
│   ├── index18.ts
│   ├── index19.ts
│   ├── index1.ts
│   ├── index2.ts
│   ├── index3.ts
│   ├── index4.ts
│   ├── index5.ts
│   ├── index6.ts
│   ├── index7.ts
│   ├── index8.ts
│   └── index9.ts
├── 2x1
│   ├── index0.ts
│   ├── index10.ts
│   ├── index11.ts
│   ├── index12.ts
│   ├── index13.ts
│   ├── index14.ts
│   ├── index15.ts
│   ├── index16.ts
│   ├── index17.ts
│   ├── index18.ts
│   ├── index19.ts
│   ├── index1.ts
│   ├── index2.ts
│   ├── index3.ts
│   ├── index4.ts
│   ├── index5.ts
│   ├── index6.ts
│   ├── index7.ts
│   ├── index8.ts
│   └── index9.ts
└── 4x3
    ├── index0.ts
    ├── index10.ts
    ├── index11.ts
    ├── index12.ts
    ├── index13.ts
    ├── index14.ts
    ├── index15.ts
    ├── index16.ts
    ├── index17.ts
    ├── index18.ts
    ├── index19.ts
    ├── index1.ts
    ├── index2.ts
    ├── index3.ts
    ├── index4.ts
    ├── index5.ts
    ├── index6.ts
    ├── index7.ts
    ├── index8.ts
    └── index9.ts

...

{
  "name":"test"
}

{
  "offset":0,
  "size":10
}

[{
    "id": "test",
    "streamName": "test",
    "status": "ACTIVE",
    "waitingSize": 0,
    "profiles": [
      "a_test",
      "v_test"
    ],
    "subscribers": 1,
    "playlist": "...",
    "createdDate": 1697605114475,
    "logs": []
}]

{
  "name":"test"
}

{
  "hlsId":"test",
  "profileName":"v_test" }

{
  "name": "v_test",
  "stream": {
    "appKey": "defaultApp",
    "sessionId": "test-HLS",
    "mediaSessionId": "81b8b278-612e-4b72-9153-454be9df0a34-test-HLS",
    "name": "test",
    "published": false,
    "hasVideo": false,
    "hasAudio": true,
    "status": "PLAYING",
    "sdp": "...",
    "videoCodec": "H264",
    "record": false,
    "width": 1280,
    "height": 720,
    "bitrate": 0,
    "minBitrate": 0,
    "maxBitrate": 0,
    "quality": 0,
    "parentMediaSessionId": "f3401d2e-7e9a-4e18-a353-d323c947ac94",
    "history": false,
    "gop": 0,
    "fps": 0,
    "audioBitrate": 0,
    "codecImpl": "",
    "transport": "UDP",
    "cvoExtension": true,
    "createDate": 1697605114875,
    "mediaType": "play",
    "audioState": {
      "muted": false
    },
    "videoState": {
      "muted": false
    },
    "mediaProvider": "HLS"
  },
  "keyFrameReceived": true,
  "videoProfile": {
    "type": "video",
    "width": 1280,
    "height": 720,
    "fps": 29,
    "bitrate": 1720,
    "codec": "",
    "quality": 0,
    "audioGroupId": "audio"
  },
  "metrics": {
    "minFPS": 29.962547,
    "avgFPS": 30.000088,
    "maxFPS": 30.04292,
    "countGaps": 0,
    "resolutionChanges": 0,
    "queueSize": 10,
    "startPts": 375400,
    "currentPts": 375400
  },
  "subscribers": 1
}

{
  "hlsId":"test"
}

[
  {
    "id": "192.168.0.83-59000-Mozilla/5.0 (X11; Linux x86_64) Chrome/118.0.0.0",
    "ip": "192.168.0.83",
    "port": 59000,
    "userAgent": "Mozilla/5.0 (X11; Linux x86_64) Chrome/118.0.0.0",
    "active": true,
    "metrics": {
      "profileTime": {
        "test": 71,
        "v_test": 541353
      },
      "requestsNumber": 5930,
      "requestsStatuses": {
        "200 OK": 5930
      },
      "profileSwitches": 1,
      "maxResponseTime": 29,
      "minResponseTime": 0,
      "avgResponseTime": 0.4436762225969646
    }
  }
]

Parameters

...

Description

...

Example

...

name

...

Stream published name

...

test

...

Issues

1. If HLS agent for the stream is started by REST query /hls/startup, and there are no active HLS subscribers, agent will stop after the following timeout in seconds

hls_manager_provider_timeout=300

By default, the timeout is 5 minutes. Also it concerns HLS agents which are started automatically for streams published using the following parameter

hls_auto_start=true

2. If HLS agent for the stream is stopped by REST query /hls/terminate, and there are active HLS subscribers, this agent will be restarted. In this case, active HLS subscribers must reconnect to the stream.

LL HLS stream issues displaying

...

{
  "offset":0,
  "size":10
}

[
  {
    "ip": "192.168.0.83",
    "port": 51708,
    "userAgent": "Chrome/125.0.0.0 Safari/537.36"
  }
]

{
  "ids": [
    "test",
    "test-HLS-ABR-STREAM"
  ]
}

{
  

...

"

...

ids": 

...

[
    "

...

test",
    "

...

test-HLS-ABR-STREAM"
  ]
}

Parameters

Issues

1. If HLS agent for the stream is started by REST query /hls/startup, and there are no active HLS subscribers, agent will stop after the following timeout in seconds

hls_manager_provider_timeout=300

By default, the timeout is 5 minutes. Also it concerns HLS agents which are started automatically for streams published using the following parameter

hls_auto_start=true

2. If HLS agent for the stream is stopped by REST query /hls/terminate, and there are active HLS subscribers, this agent will be restarted. In this case, active HLS subscribers must reconnect to the stream.

LL HLS stream issues displaying

Since build 5.2.1709 LL HLS stream issues are displaying in response on /hls/find_all REST API query:

{
   "test": {
    "handler": "com.flashphoner.server.client.handler.wcs4.WCS4Handler@74dbf27b",
    "state": "ACTIVE",
    "writer": "HLS-test",
    "streamStatus": "PLAYING",
    "writerStarted": "true",
    "logs": [
      "2023-07-18T10:22:52.457 WARNING: Playback speed changed to 0.779, segment 49, media type: video",
      ..."2023-07-18T10:22:56.614 WARNING: Gap{from=112000, to=114000, duration=2000}, media type: video",
    ]
  }
}

...

  "2023-07-18T10:22:56.615 WARNING: Fps changed from 30 to 27, segment 50 , media type: video",
      "2023-07-18T10:22:56.624 WARNING: Segment 51.1 have no data, pts 112400, duration 400, media type: video",
      ...
    ]
  }
}

By default, up to 50 last issues are displayed for every stream. This value may be changed with the following parameter

...

Where 8445 is HTTPS HLS port of WCS server

HLS ABR support

For a streams with video track (video only or audio+video) WCS supports HLS ABR in CDN (a qualities are encoded on a dedicated Transcoder node) and on a single node.

Legacy HLS ABR implementation in builds 5.2.484 - 5.2.582

Since build 5.2.484 HLS ABR playlists support was added. This feature can be enabled with the following parameter

hls_master_playlist_enabled=true

Master playlist file name can be set using the following parameter

hls_manifest_file=index.m3u8

Browser should get master playlist by URL

https://wcs_address:8445/streamName/index.m3u8

Where

• wcs_address - WCS server address
• streamName - stream name
• index.m3u8 - master playlist file name

When master playlist is requested for the stream, server checks if streams are published according to transcoding profiles listed in cdn_profiles.yml file, for example:

profiles:
  -720p:
    video:
      height: 720
      bitrate: 1000
      codec: h264
  -480p:
    video:
      height: 480
      bitrate: 1000
      codec: h264
  -240p:
    video:
      height: 240
      bitrate: 400
      codec: h264

All the streams published by profiles on server, will be added to master playlist, for example:

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
../streamName-720p/streamName-720p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=852x480,CODECS="avc1.42e01f,mp4a.40.2"
../streamName-480p/streamName-480p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=400000,RESOLUTION=426x240,CODECS="avc1.42e01f,mp4a.40.2"
../streamName-240p/streamName-240p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
../streamName/streamName.m3u8

Then browser switches between HLS streams listed in master playlist depending on channel bandwidth.

To provide HLS streams by profiles, the following should be done:

1. On a standalone server:

1.1. Periodically check if streams are transcoded to parameters set by profiles, and launch transcoding if necessary using REST API

	curl -s -X POST -d "{\"uri\":\"transcoder://tcode_test-240p\",\"remoteStreamName\":\"test\",\"localStreamName\":\"test-240p\",\"encoder\":{\"width\":320,\"height\":240}}" http://localhost:8081/rest-api/transcoder/startup
	curl -s -X POST -d "{\"uri\":\"transcoder://tcode_test-480p\",\"remoteStreamName\":\"test\",\"localStreamName\":\"test-480p\",\"encoder\":{\"width\":640,\"height\":480}}" http://localhost:8081/rest-api/transcoder/startup
	curl -s -X POST -d "{\"uri\":\"transcoder://tcode_test-720p\",\"remoteStreamName\":\"test\",\"localStreamName\":\"test-720p\",\"encoder\":{\"width\":1280,\"height\":720}}" http://localhost:8081/rest-api/transcoder/startup

1.2. Periodically launch HLS cut for the streams, for example

curl -s -X POST -d "{\"name\":\"test\"}" http://localhost:8081/rest-api/hls/startup
sleep 1
curl -s -X POST -d "{\"name\":\"test-240p\"}" http://localhost:8081/rest-api/hls/startup
sleep 1
curl -s -X POST -d "{\"name\":\"test-480p\"}" http://localhost:8081/rest-api/hls/startup
sleep 1
curl -s -X POST -d "{\"name\":\"test-720p\"}" http://localhost:8081/rest-api/hls/startup

2. On an Edge server in CDN periodically request HLS streams by transcoding profiles, for example

curl -s http://localhost:8082/test/test.m3u8
sleep 1
curl -s http://localhost:8082/test-240p/test-240p.m3u8
sleep 1
curl -s http://localhost:8082/test-480p/test-480p.m3u8
sleep 1
curl -s http://localhost:8082/test-720p/test-720p.m3u8
sleep 1

Actual HLS ABR implementation in build 5.2.585 and newer

Since build 5.2.585 HLS ABR implementation is significally changed. As usual, HLS ABR can be used in CDN only, but Edge server captures all the transcoded streams for ABR manifest stream variants within the same mediasession to syhchronize the stream variants. This requires to configure Tanscoder nodes and Edge nodes simultaneously, and adds some limits. Let's explore it below.

Transcoder node settings

To synchronize all the variants of the same stream, encoding should be aligned on Transcoder node

transcoder_align_encoders=true

Also, FPS filter should be enabled

video_filter_enable_fps=true
video_filter_fps=25

All stream variants key frames (GOPs) should be synchronized. For example, we will send key frame every 2 seconds for 25 fps stream

video_filter_fps_gop_synchronization=50

HLS Edge node settings

HLS preloader and streams resizing should be disabled on HLS Edge node

hls_preloader_enabled=false
hls_player_width=0
hls_player_height=0

The transcoding profiles should be set as follows in cdn_profiles.yml file

profiles:
 -240p:
  audio:
    codec : mpeg4-generic
    rate : 48000
  video:
    height : 240
    bitrate : 300
    gop : 50
    codec : h264
 -480p:
  video:
    height : 480
    bitrate : 600
    gop : 50
    codec : h264
 -720p:
  video:
    height : 720
    bitrate : 1000
    gop : 50
    codec : h264

Note that audio parameters can be set for the first profile only because those parameters should be identical for all the profiles, and will be applyed according to the first profile.

Then HLS ABR should be enabled

hls_abr_enabled=true

Usage

Client should request ABR manifest giving a stream name with a special suffix

https://server:8445/test_0-HLS-ABR-STREAM/test_0-HLS-ABR-STREAM.m3u8

The suffix can be set with the following parameter

hls_abr_stream_name_suffix=-HLS-ABR-STREAM

The playlist contains links to stream variants playlists, a client can switch between then

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=614400,RESOLUTION=852x480,CODECS="avc1.42e01f,mp4a.40.2"
-480p/-480p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1024000,RESOLUTION=1278x720,CODECS="avc1.42e01f,mp4a.40.2"
-720p/-720p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=307200,RESOLUTION=426x240,CODECS="avc1.42e01f,mp4a.40.2"
-240p/-240p.m3u8

If stream name contains no suffix, HLS will be played without ABR support.

Transcoding to higher resolutions prevention

If stream transcoding to higher resolutions is disabled on HLS ABR Edge server

cdn_strict_transcoding_boundaries=true

then stream variants conforming to higher resolution profiles will not be cut for the stream, and will not be vailable to a player.

Known limits

1. HLS Edge can be used for HLS streaming only, client sessions of another kinds will not work.

2. Stream recording, snapshots, mixing, stream capturing from another server and other captured stream management functions will not work.

HLS ABR on a single node

In most cases, it's more convenient to use CDN to play HLS ABR, because this is more scalable solution at server performance point. However, since build 5.2.1582 it is possible to transcode a stream to a certain HLS ABR qualities on a single server

hls_abr_enabled=true
hls_abr_with_cdn=false

...

Displaying a list of HLS clients connected to the server

Since build 5.2.1968 it is possible to display a list of HLS clients connected to the server. The list is returned in response to the /hls/connections query:

[
  {
    "ip": "192.168.0.83",
    "port": 51708,
    "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36"
  }
]

Where:

• ip - client address
• port - client source port
• userAgent - User-Agent header sent by the client

For HTTPS clients all the tabs of the same browser window on the same PC will be displayed at one position because HTTP/2 uses the same TCP connection for all HTTPS connections.

A clients count in the list will be the same as the statistics page value

curl -s 'http://wcs:8081/?action=stat&params=connections_hls'

HLS stream segments recording to disk for debugging purposes

Since build 5.2.1913 it is possible to record a segments and a playlists for a certain HLS stream played by subscribers for debugging purposes. Segments will be recorded to the folder set by the following parameter

hls_debug_dir=hls-debug

Segments recording for a certain stream may be started with REST API query /hls/enableRecording 

POST /rest-api/hls/enableRecording HTTP/1.1
Host: localhost:8081
Content-Type: application/json

{
    "ids": [
        "test",
        "test-HLS-ABR-STREAM"
    ] 
}

Use the REST API query /hls/disableRecording to stop the recording

POST /rest-api/hls/disableRecording HTTP/1.1
Host: localhost:8081
Content-Type: application/json

{
    "ids": [
        "test",
        "test-HLS-ABR-STREAM"
    ] 
}

Use a various media parsing and playing tools like ffmpeg, ffprobe etc to work with a segments recorded. Also, the debud stream recording may be played from the server using the URL with -DEBUG suffix

https://wcs:8445/test-DEBUG/test-DEBUG.m3u8

If the stream with a certain name was recorded, and then a new stream was published with the same name, a new recording will overwrite the previous one.

HLS ABR support

For a streams with video track (video only or audio+video) WCS supports HLS ABR in CDN (a qualities are encoded on a dedicated Transcoder node) and on a single node.

Legacy HLS ABR implementation in builds 5.2.484 - 5.2.582

Since build 5.2.484 HLS ABR playlists support was added. This feature can be enabled with the following parameter

hls_master_playlist_enabled=true

Master playlist file name can be set using the following parameter

hls_manifest_file=index.m3u8

Browser should get master playlist by URL

https://wcs_address:8445/streamName/index.m3u8

Where

• wcs_address - WCS server address
• streamName - stream name
• index.m3u8 - master playlist file name

When master playlist is requested for the stream, server checks if streams are published according to transcoding profiles listed in cdn_profiles.yml file, for example:

profiles:
  -720p:
    video:
      height: 720
      bitrate: 1000
      codec: h264
  -480p:
    video:
      height: 480
      bitrate: 1000
      codec: h264
  -240p:
    video:
      height: 240
      bitrate: 400
      codec: h264

All the streams published by profiles on server, will be added to master playlist, for example:

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
../streamName-720p/streamName-720p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=852x480,CODECS="avc1.42e01f,mp4a.40.2"
../streamName-480p/streamName-480p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=400000,RESOLUTION=426x240,CODECS="avc1.42e01f,mp4a.40.2"
../streamName-240p/streamName-240p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
../streamName/streamName.m3u8

Then browser switches between HLS streams listed in master playlist depending on channel bandwidth.

To provide HLS streams by profiles, the following should be done:

1. On a standalone server:

1.1. Periodically check if streams are transcoded to parameters set by profiles, and launch transcoding if necessary using REST API

	curl -s -X POST -d "{\"uri\":\"transcoder://tcode_test-240p\",\"remoteStreamName\":\"test\",\"localStreamName\":\"test-240p\",\"encoder\":{\"width\":320,\"height\":240}}" http://localhost:8081/rest-api/transcoder/startup
	curl -s -X POST -d "{\"uri\":\"transcoder://tcode_test-480p\",\"remoteStreamName\":\"test\",\"localStreamName\":\"test-480p\",\"encoder\":{\"width\":640,\"height\":480}}" http://localhost:8081/rest-api/transcoder/startup
	curl -s -X POST -d "{\"uri\":\"transcoder://tcode_test-720p\",\"remoteStreamName\":\"test\",\"localStreamName\":\"test-720p\",\"encoder\":{\"width\":1280,\"height\":720}}" http://localhost:8081/rest-api/transcoder/startup

1.2. Periodically launch HLS cut for the streams, for example

curl -s -X POST -d "{\"name\":\"test\"}" http://localhost:8081/rest-api/hls/startup
sleep 1
curl -s -X POST -d "{\"name\":\"test-240p\"}" http://localhost:8081/rest-api/hls/startup
sleep 1
curl -s -X POST -d "{\"name\":\"test-480p\"}" http://localhost:8081/rest-api/hls/startup
sleep 1
curl -s -X POST -d "{\"name\":\"test-720p\"}" http://localhost:8081/rest-api/hls/startup

2. On an Edge server in CDN periodically request HLS streams by transcoding profiles, for example

curl -s http://localhost:8082/test/test.m3u8
sleep 1
curl -s http://localhost:8082/test-240p/test-240p.m3u8
sleep 1
curl -s http://localhost:8082/test-480p/test-480p.m3u8
sleep 1
curl -s http://localhost:8082/test-720p/test-720p.m3u8
sleep 1

Actual HLS ABR implementation in build 5.2.585 and newer

Since build 5.2.585 HLS ABR implementation is significally changed. As usual, HLS ABR can be used in CDN only, but Edge server captures all the transcoded streams for ABR manifest stream variants within the same mediasession to syhchronize the stream variants. This requires to configure Tanscoder nodes and Edge nodes simultaneously, and adds some limits. Let's explore it below.

Transcoder node settings

To synchronize all the variants of the same stream, encoding should be aligned on Transcoder node

transcoder_align_encoders=true

Also, FPS filter should be enabled

video_filter_enable_fps=true
video_filter_fps=25

All stream variants key frames (GOPs) should be synchronized. For example, we will send key frame every 2 seconds for 25 fps stream

video_filter_fps_gop_synchronization=50

HLS Edge node settings

HLS preloader and streams resizing should be disabled on HLS Edge node

hls_preloader_enabled=false
hls_player_width=0
hls_player_height=0

FPS equalizing The transcoding profiles should also be enabledbe set as follows in cdn_profiles.yml file

transcoder_align_encoders=true 
video_filter_enable_fps=true
video_filter_fps=30
video_filter_fps_gop_synchronization=60

HLS ABR transcoding quality profiles should be set in /usr/local/FlashphonerWebCallServer/conf/hls_abr_profiles.yml file

profiles:
  -180p:
    audio:
  profiles:
 -240p:
  audio:
    codec : mpeg4-generic
      rate : 48000
    video:
      height : 180240
      bitrate : 300
    gop : 50
    codec : h264
 -480p:
  video:
    codecImplheight : OPENH264480
    bitrate : 600
    gop : 6050
    codec  fps : 30
 h264
  -240p720p:
    audiovideo:
    height  codec : mpeg4-generic720
    bitrate  rate : 480001000
    video:
      height : 240
      bitrate : 500gop : 50
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30
 
  -480p:
    audio:
      codec : mpeg4-generic
      rate : 48000
    video:
      height : 480
      bitrate : 1000
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30
 
  -720p:
    audio:
      codec : mpeg4-generic
      rate : 48000
    video:
      height : 720
      bitrate : 1500
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

...

Note that audio parameters can be set for the first profile only because those parameters should be identical for all the profiles, and will be applyed according to the first profile.

Then HLS ABR should be enabled

hls_abr_enabled=true

Usage

Client should request ABR manifest giving a stream name with a special suffix

https://server:8445/test_0-HLS-ABR-STREAM/test_0-HLS-ABR-STREAM.m3u8

The suffix can be set with the following parameter

hls_abr_stream_name_suffix=-HLS-ABR-STREAM

The playlist contains links to stream variants playlists, a client can switch between then

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=614400,RESOLUTION=852x480,CODECS="avc1.42e01f,mp4a.40.2"
-480p/-480p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1024000,RESOLUTION=1278x720,CODECS="avc1.42e01f,mp4a.40.2"
-720p/-720p.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=307200,RESOLUTION=426x240,CODECS="avc1.42e01f,mp4a.40.2"
-240p/-240p.m3u8

If stream name contains no suffix, HLS will be played without ABR support.

Transcoding to higher resolutions prevention

If stream transcoding to higher resolutions is disabled on HLS ABR Edge server

hlscdn_ll_enabled=true
hls_new_http_stack=true

Transcoding to higher resolutions prevention

Since build 5.2.1611, if a stream published has a less picture height than some profiles listed in hls_abr_profiles.yml, then all the variants with higher resolutions will not be encoded and will not be included to manfest. For example, the manifest will look as follows when original stream has  960x540 resolution:

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=300000,RESOLUTION=320x180,CODECS="avc1.42e01f,mp4a.40.2"
180/180.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=500000,RESOLUTION=428x240,CODECS="avc1.42e01f,mp4a.40.2"
240/240.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=848x480,CODECS="avc1.42e01f,mp4a.40.2"
480/480.m3u8

because there will not be upscale to 1280x720.

If the stream resolution is lower than a minimal profile, this stream will be transcoded to the minimal available profile, and the only variant will be included to manifest

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=300000,RESOLUTION=320x180,CODECS="avc1.42e01f,mp4a.40.2"
180/180.m3u8

If there is a profile without both width and height parameters, the stream will be transcoded to its original resolution with GOP and FPS defined in the profile, and this variant will always be included to manifest:

strict_transcoding_boundaries=true

then stream variants conforming to higher resolution profiles will not be cut for the stream, and will not be vailable to a player.

Known limits

1. HLS Edge can be used for HLS streaming only, client sessions of another kinds will not work.

2. Stream recording, snapshots, mixing, stream capturing from another server and other captured stream management functions will not work.

HLS ABR on a single node

In most cases, it's more convenient to use CDN to play HLS ABR, because this is more scalable solution at server performance point. However, since build 5.2.1582 it is possible to transcode a stream to a certain HLS ABR qualities on a single server

hls_abr_enabled=true
hls_abr_with_cdn=false

In this case, HLS preloader and default transcoding must be disabled because a stream will be transcoded by defined profiles

hls_preloader_enabled=false
hls_player_width=0
hls_player_height=0

FPS equalizing should also be enabled

transcoder_align_encoders=true 
video_filter_enable_fps=true
video_filter_fps=30
video_filter_fps_gop_synchronization=60

HLS ABR transcoding quality profiles should be set in /usr/local/FlashphonerWebCallServer/conf/hls_abr_profiles.yml file

profiles:
  original-180p:
    videoaudio:
      codec : h264 mpeg4-generic
      rate : 48000
    video:
      codecImplheight : OPENH264180
      gopbitrate : 60300
      fpscodec : 30

Qualities order in HLS ABR manifest

Before build 5.2.1606, HLS ABR manifest qualities are sorted in profile names alphabetical order, for example, such cdn_profiles.yml or hls_abr_profiles.yml 

profiles:
  360:
    video:h264
      codecImpl : OPENH264
      heightgop : 36060
      bitratefps : 100030
 
     codec : h264-240p:
      codecImpl : OPENH264audio:
      gopcodec : 60mpeg4-generic
      fpsrate : 3048000

  720:
    video:
      height : 720240
      bitrate : 2000500
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30
 
  -480p:
    audio:
      codec : mpeg4-generic
  1080:    rate : 48000
    video:
      height : 480
      bitrate : 1000
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30
 
  -720p:
    audio:
      codec : mpeg4-generic
      rate : 48000
    video:
      height : 720
      bitrate : 1500
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

Low Latency HLS is also supported for HLS ABR

hls_ll_enabled=true
hls_new_http_stack=true

Transcoding to higher resolutions prevention

Since build 5.2.1611, if a stream published has a less picture height than some profiles listed in hls_abr_profiles.yml, then all the variants with higher resolutions will not be encoded and will not be included to manfest. For example, the manifest will look as follows when original stream has  960x540 resolution:

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=300000,RESOLUTION=320x180,CODECS="avc1.42e01f,mp4a.40.2"
180/180.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=500000,RESOLUTION=428x240,CODECS="avc1.42e01f,mp4a.40.2"
240/240.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=848x480,CODECS="avc1.42e01f,mp4a.40.2"
480/480.m3u8

because there will not be upscale to 1280x720.

If the stream resolution is lower than a minimal profile, this stream will be transcoded to the minimal available profile, and the only variant will be included to manifest

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=300000,RESOLUTION=320x180,CODECS="avc1.42e01f,mp4a.40.2"
180/180.m3u8

If there is a profile without both width and height parameters, the stream will be transcoded to its original resolution with GOP and FPS defined in the profile, and this variant will always be included to manifest:

profiles:
  original:
    video:
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

Qualities order in HLS ABR manifest

Before build 5.2.1606, HLS ABR manifest qualities are sorted in profile names alphabetical order, for example, such cdn_profiles.yml or hls_abr_profiles.yml 

profiles:
  360:
    video:
      height : 360
      bitrate : 1000
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

  720:
    video:
      height : 720
      bitrate : 2000
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

  1080:
    video:
      height : 1080
      bitrate : 2500
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

give the following manifest

#EXTM3U
      bitrate : 2500
      codec : h264
      codecImpl : OPENH264
      gop : 60
      fps : 30

give the following manifest

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1920x1080,CODECS="avc1.42e01f,mp4a.40.2"
1080/1080.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8

Since build 5.2.1606, manifest qualities order equals to profiles order in cdn_profiles.yml or hls_abr_profiles.yml

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1920x1080,CODECS="avc1.42e01f,mp4a.40.2"
1080/1080.m3u8

If there are two profiles with the same name in the setup, server will use only the last profile with the same name.

Force transcoding of a maximum ABR quality only if there are B-frames in a source stream

To reduce a server load while video encoding, since WCS build 5.2.1840 it is possible to transcode a maximum ABR quality (which is usually the original stream resolution and bitrate) only if there are B-frames in a source stream. The feature may be enabled by the following parameter

h264_b_frames_force_transcoding=true

In this case the server will detect B-frames in a stream analizing a certain frames count (10 by default)

frame_cnt_to_determine_their_type=10

If there are B-frames in the stream, the maximum ABR quality will be transcoded and will be available for playback in the HLS manifest

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1920x1080,CODECS="avc1.42e01f,mp4a.40.2"
1080/1080.m3u8

If there are no B-frames in the stream, the maximum ABR quality will not be transcoded

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8

The original quality should be requested separately from a playing client.

Since build 5.2.1606, manifest qualities order equals to profiles order in cdn_profiles.yml or hls_abr_profiles.yml.1916, the feature is available for HLS ABR in CDN. To activate it, all the CDN servers should be updated to build 5.2.1916 or newer, and the following parameters should be set on Edge server

cdn_strict_transcoding_boundaries=true
h264_b_frames_force_transcoding=true

Maximum playlist size

Maximum playlist size in segments is defined by the following parameter

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1920x1080,CODECS="avc1.42e01f,mp4a.40.2"
1080/1080.m3u8

If there are two profiles with the same name in the setup, server will use only the last profile with the same name.

Force transcoding of a maximum ABR quality only if there are B-frames in a source stream

...

hls_list_size=8

By default, HLS playlist size is 8 segments. Note that HLS cut is just started, a segments quantity in the first playlists will be less than value set.

HLS segments storage

Using disk

In builds before 5.2.1713HLS segments are written to server hard drive to the /usr/local/FlashphonerWebCallServer/hls  folder by default. Starting from build 5.2.687, the folder for saving segments can be changed using the following parameter

hls_dir=/usr/local/FlashphonerWebCallServer/hls

(Preloader folder is configured separately with parameter hls_preloader_dir.)

The number of stored segments corresponds to the specified playlist size. The less segments number, the less playback latency. However subscribers with poor channel could request HLS segments which are already gone from playlist and disk if playlist is short. To fix it, since build 5.2.581 the certain number of segments can be stored on disk after they gone from playlist. This feature can be enabled by the following parameter

hls_hold_segments_before_delete=true

By default, 5 last segments will be stored

h264hls_bhold_framessegments_force_transcodingsize=true

...

5

For example, if playlist contains 3 segments

frame_cnt_to_determine_their_type=10

...

#EXTM3U
#EXT-X-VERSION:8
#EXT-X-TARGETDURATION:11
#EXT-X-MEDIA-SEQUENCE:15
#EXT-X-DISCONTINUITY-SEQUENCE:1
#EXTINF:3.415,
test_017.ts
#EXTINF:10.417,
test_018.ts
#EXTINF:9.084,
test_019.ts

3 current segments and 5 previous segments will be stored on disk

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1920x1080,CODECS="avc1.42e01f,mp4a.40.2"
1080/1080.m3u8

If there are no B-frames in the stream, the maximum ABR quality will not be transcoded

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,CODECS="avc1.42e01f,mp4a.40.2"
360/360.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720,CODECS="avc1.42e01f,mp4a.40.2"
720/720.m3u8

The original quality should be requested separately from a playing client.

Maximum playlist size

Maximum playlist size in segments is defined by the following parameter

hls_list_size=8

By default, HLS playlist size is 8 segments. Note that HLS cut is just started, a segments quantity in the first playlists will be less than value set.

HLS segments storage

Using disk

...

hls_dir=/usr/local/FlashphonerWebCallServer/hls

(Preloader folder is configured separately with parameter hls_preloader_dir.)

The number of stored segments corresponds to the specified playlist size. The less segments number, the less playback latency. However subscribers with poor channel could request HLS segments which are already gone from playlist and disk if playlist is short. To fix it, since build 5.2.581 the certain number of segments can be stored on disk after they gone from playlist. This feature can be enabled by the following parameter

hls_hold_segments_before_delete=true

...

test_012.ts
test_013.ts
test_014.ts
test_015.ts
test_016.ts
test_017.ts
test_018.ts
test_019.ts

Using memory

Under high load, for example on HLS streaming dedicated server, segments reading from hard drive to send them to subscribers can increase the latency. In this case, HLS segments storing in memory should be enabled

hls_store_segment_in_memory=true

Segments will be read from memory to send them to subscribers. Note this will require more Java heap memory.

Since build 5.2.1713 HLS segments are stored in memory by default.

Debug logs for HLS session

For an error report, debug logging can be enabled for HLS sessions using CLI

update node-setting --value true hls_enable_session_debug

Note that config flashphoner.properties will be overwritten after the command.

Low Latency HLS support

Since WCS build 5.2.1181, Low Latency HLS (LL HLS) is supported. The feature may be enabled with the following parameters

hls_ll_enabled=true
hls_new_http_stack=true

In this case, players supporting LL HLS (HLS.JS for example) will play additional HLS segments reducing playback latency comparing with players which do not play those segments (VideoJS for example).

It is necessary to provide a stable FPS and keyframe interval for a published stream to play it as LL HLS correctly. Therefore, it is recommended to publish the source strem as RTMP with the following example parameters

Image Added

Image Added

Recommended settings for LL HLS playback

Since build 5.2.1345, the recommended settings to play Low latency HLS are follow:

hls_ll_enabled=true
hls_auto_start=true
hls_preloader_enabled=false
hls_player_width=848
hls_player_height=480
video_filter_enable_fps=true
video_filter_fps=30
video_encoder_h264_gop=60

Since build 5.2.1965, the following parameter is enough to play LL HLS, a defaults may be used for other settings

hls_holdll_segments_sizeenabled=5

For example, if playlist contains 3 segments

#EXTM3U
#EXT-X-VERSION:8
#EXT-X-TARGETDURATION:11
#EXT-X-MEDIA-SEQUENCE:15
#EXT-X-DISCONTINUITY-SEQUENCE:1
#EXTINF:3.415,
test_017.ts
#EXTINF:10.417,
test_018.ts
#EXTINF:9.084,
test_019.ts

...

true

Using HTTP/2 and HTTP/1

According to specification, LL HLS must be played using HTTP/2, i.e. via secure connection

test_012.ts
test_013.ts
test_014.ts
test_015.ts
test_016.ts
test_017.ts
test_018.ts
test_019.ts

Using memory

...

https://wsc:8445/test/test.m3u8

It is also possible to use HTTP/1 via unsecure connection with WCS

http://wsc:8082/test/test.m3u8

Note that LL HLS via HTTP/1 works in main browsers except Safari, and this feature is not recommended to use in production.

LL HLS segments folder

By default, LL HLS segments are written to streams subdolder to the folder

hls_store_segment_in_memory=true

Segments will be read from memory to send them to subscribers. Note this will require more Java heap memory.

Since build 5.2.1713 HLS segments are stored in memory by default.

Debug logs for HLS session

...

ll_hls_dir=/usr/local/FlashphonerWebCallServer/ll-hls

If folder has changed

ll_hls_dir=/opt/ll-hls

it is necessary to set file access permissions using the command

update node-setting --value true hls_enable_session_debug

Note that config flashphoner.properties will be overwritten after the command.

Low Latency HLS support

...

/usr/local/FlashphonerWebCallServer/bin/webcallserver set-permissions

and restart WCS to apply the changes.

Maximum LL HLS playlist size

Maximum LL HLS playlist size in segments is defined by the following parameter

ll_hls_list_size=12

By default, LL HLS playlist size is 12 full segments. Note that LL HLS cut is just started, a full segments quantity in the first playlists will be less than value set.

LL HLS preloader

Since build 5.2.1181, Low Latency HLS (LL HLS) is supported. The feature may be enabled with the following parameters1729, a special preloader can be used for LL HLS as like as usual HLS

hls_llpreloader_enabled=true
hls_new_http_stack=true

In this case, players supporting LL HLS (HLS.JS for example) will play additional HLS segments reducing playback latency comparing with players which do not play those segments (VideoJS for example).

It is necessary to provide a stable FPS and keyframe interval for a published stream to play it as LL HLS correctly. Therefore, it is recommended to publish the source strem as RTMP with the following example parameters

Image Removed

Image Removed

Recommended settings for LL HLS playback

Since build 5.2.1345, the recommended settings to play Low latency HLS are follow:LL HLS preloader files are placed by default to the folder

ll_hls_preloader_dir=/usr/local/FlashphonerWebCallServer/ll-hls/.preloader

The folder can be changed, for example

hls_ll_enabled=true
hls_auto_start=true
hls_preloader_enabled=false
hls_player_width=848
hls_player_height=480
video_filter_enable_fps=true
video_filter_fps=30
video_encoder_h264_gop=60

Using HTTP/2 and HTTP/1

...

dir=/opt/preloader

Default LL HLS preloader consists of the following files, one per each standard video streams aspect ratio

https://wsc:8445/test/test.m3u8

...

16x9.mp4
2x1.mp4
4x3.mp4

If stream aspect ration is unknown, 16:9 preloader file will be used. If there are no preloader files at all, LL HLS stream cut will start without a preloader like

http://wsc:8082/test/test.m3u8

Note that LL HLS via HTTP/1 works in main browsers except Safari, and this feature is not recommended to use in production.

LL HLS segments folder

By default, LL HLS segments are written to streams subdolder to the folder

ll_hls_dir=/usr/local/FlashphonerWebCallServer/ll-hls

If folder has changed

ll_hls_dir=/opt/ll-hls

...

hls_preloader_enabled=false

Custom LL HLS preloader setup

A custom LL HLS preloader can be set up if necessary. The media files in three standard aspects 16:9, 4:3 и 2:1 should be prepared according to the following requirements:

• MP4 container, video codec H264, audio codec AAC
• the files should allow instant playback (MP4 moov atom must precede mdat one)
• the files should not containt B frames
• the file duration should be near 1 minute
• the file should have a smooth FPS
• keyframe interval should be near 2 seconds

Suppose a source files are prepared in a proper aspects in OBS Studio or in a video editor. Use the following command example to convert a preloader files to conform the requirements above:

/usr/local/FlashphonerWebCallServer/bin/webcallserver set-permissions

and restart WCS to apply the changes.

Maximum LL HLS playlist size

Maximum LL HLS playlist size in segments is defined by the following parameter

ll_hls_list_size=12

By default, LL HLS playlist size is 12 full segments. Note that LL HLS cut is just started, a full segments quantity in the first playlists will be less than value set.

LL HLS preloader

Since build 5.2.1729, a special preloader can be used for LL HLS as like as usual HLS

hls_preloader_enabled=true

LL HLS preloader files are placed by default to the folder

ll_hls_preloader_dir=/usr/local/FlashphonerWebCallServer/ll-hls/.preloader

...

ffmpeg -i 16x9-source.mp4 -bf 0 -acodec aac -vcodec h264 -preset ultrafast -g 60 -strict -2 -r 30 -ar 48000 -movflags faststart -ss 00:00:00 -t 00:01:00 16x9.mp4

Then the default preloader files should be replaced by custom preloader files, and WCS should be restarted.

To restore default preloader it is enough to remove custom preloader files and restart WCS.

A settings applied both for LL and non-LL HLS

Since build 5.2.1965 all the settings with hls_ prefix are applied both to LL and non-LL HLS.

The following parameters are applied to LL HLS only and not applied to non-LL HLS

m4s container support

Since build 5.2.1626 m4s container is supported for HLS segments cut, and since build 5.2.1632 the container is enabled by default for HLS ABR too

ll_hls_preloaderfragmented_dir=/opt/preloader

...

mp4=true

Since build 5.2.1724, m4s container is supported for HLS ABR in CDN.

You can switch back to the ts container if necessary

16x9.mp4
2x1.mp4
4x3.mp4

...

ll_hls_fragmented_mp4=false

Using a common network stack for HLS and Low Latency HLS

Since build 5.2.1749 the parameter allowing an unified network stack usage both for HLS and Low latency HLS is added. The parameter is enabled by default:

hlsuse_preloadernew_enabled=false

Custom LL HLS preloader setup

A custom LL HLS preloader can be set up if necessary. The media files in three standard aspects 16:9, 4:3 и 2:1 should be prepared according to the following requirements:

• MP4 container, video codec H264, audio codec AAC
• the files should allow instant playback (MP4 moov atom must precede mdat one)
• the files should not containt B frames
• the file duration should be near 1 minute
• the file should have a smooth FPS
• keyframe interval should be near 2 seconds

Suppose a source files are prepared in a proper aspects in OBS Studio or in a video editor. Use the following command example to convert a preloader files to conform the requirements above:

ffmpeg -i 16x9-source.mp4 -bf 0 -acodec aac -vcodec h264 -preset ultrafast -g 60 -strict -2 -r 30 -ar 48000 -movflags faststart -ss 00:00:00 -t 00:01:00 16x9.mp4

Then the default preloader files should be replaced by custom preloader files, and WCS should be restarted.

To restore default preloader it is enough to remove custom preloader files and restart WCS.

m4s container support

Since build 5.2.1626 m4s container is supported for HLS segments cut, and since build 5.2.1632 the container is enabled by default for HLS ABR too

ll_hls_fragmented_mp4=true

Since build 5.2.1724, m4s container is supported for HLS ABR in CDN.

You can switch back to the ts container if necessary

ll_hls_fragmented_mp4=false

Using a common network stack for HLS and Low Latency HLS

Since build 5.2.1749 the parameter allowing an unified network stack usage both for HLS and Low latency HLS is added. The parameter is enabled by default:

use_new_hls=true

In this case:

• m4s container is used by default to record an HLS segments
• parameters with hls prefix are applied both to HLS and LL HLS
• parameters with ll_hls prefox are applied to LL HLS and to m4s container

Manifest URL setup

...

hls=true

In this case:

• m4s container is used by default to record an HLS segments
• parameters with hls prefix are applied both to HLS and LL HLS
• parameters with ll_hls prefox are applied to LL HLS and to m4s container

Manifest URL setup

Since build 5.2.1852, an URL templates to request a stream main playlist (manifest) may be customized. By default, the following templates are used:

hls_path_template={streamName}/{streamName}.m3u8
hls_abr_path_template={streamName}{abrSuffix}/{streamName}{abrSuffix}.m3u8

Where:

• streamName - stream published name
• abrSuffix - HLS ABR stream suffix set by hls_abr_stream_name_suffix parameter

In this case, the following URLs should be used to get HLS manifest

https://wcs:8445/stream/stream.m3u8

and to get HLS ABR manifest

https://wcs:8445/stream-HLS-ABR-STREAM/stream-HLS-ABR-STREAM.m3u8

For example, if a fixed manifest name different for HLS ABR and non-ABR streams is preferred to use, then the following templates should be set

hls_path_template={streamName}/playlist.m3u8
hls_abr_path_template={streamName}/playlist{abrSuffix}.m3u8

In this case, the following URLs should be used to get HLS manifest

https://wcs:8445/stream/playlist.m3u8

and to get HLS ABR manifest

https://wcs:8445/stream/playlist-HLS-ABR-STREAM.m3u8

HLS provider shutdown when source stream is stopped

Since build 5.2.1920 it is possible to control HLS provider shutdown when a source stream publishing on the server is stopped. By default, the HLS provider is stopped with a delay

hls_delayed_shutdown=true

The delay depends on playlist size

hls_list_size=8

Thus, a subscribers playing the HLS stream may play a rest of playlist if the source stream is stopped.

The delayed shutdown may be disabled if needed

hls_pathdelayed_template={streamName}/{streamName}.m3u8
hls_abr_path_template={streamName}{abrSuffix}/{streamName}{abrSuffix}.m3u8

Where:

• streamName - stream published name
• abrSuffix - HLS ABR stream suffix set by hls_abr_stream_name_suffix parameter

...

shutdown=false

In this case HLS provider will be stopped right after the source stream is stopped.

HLS segments size control

By default HLS segments will be cut either by key frame receiving or by reaching the size set by the following parameter (2000 ms by default)

https://wcs:8445/stream/stream.m3u8

and to get HLS ABR manifest

https://wcs:8445/stream-HLS-ABR-STREAM/stream-HLS-ABR-STREAM.m3u8

...

hls_time_min=2000

Since build 5.2.1974 it is possible to enable HLS segments cutting by key frame receiving only

hls_path_template={streamName}/playlist.m3u8
hls_abr_path_template={streamName}/playlist{abrSuffix}.m3u8always_start_segment_with_key_frame=true

In this case , the following URLs should be used to get HLS manifesta segment size may exceed hls_time_min value, bur a minimal segment size may be less. The following parameter is used to strictly limit the minimal segments size

https://wcs:8445/stream/playlist.m3u8

and to get HLS ABR manifest

https://wcs:8445/stream/playlist-HLS-ABR-STREAM.m3u8hls_keep_min_segment_duration=true

In this case a segment size will not be less than hls_time_min.

Known issues

1. Non-recoverable freeze of HLS stream played in iOS Safari through a CDN

...

Solution: since build 5.2.1690, use m4s container for audio only streams

13. Encoder resources leak may appear under a high load when using HLS ABR

Symptoms: when HLS ABR is used and server CPU load is high (for instance, an encoding profiles number for all the streams published exceeds CPU capabilities), encoding resources may not be freed after publishing is stopped, and this may be visible on server statistics page, for example

streams_hls=0
...
native_resources.video_encoders=5

Solution: update WCS to build 5.2.1947 and set the following parameter

handler_async_disconnect=false