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Since build 5.2.1012 it is possible to record multiple streams to one file. Then streams can be extracted from this file and mixed by a special tool. Multiple streams can be recorded only to MP4 container (H264 + AAC)or, since build 5.2.1440, to MKV container. This feature is intended, for example, to record a video conference. In this case, unlike to to MCU mixer, stream mixing works while recording file is post-processed, this allows to aquire a less of server resources during the conference itself.

Multiple stream recording is managed by REST API.

Codecs support

MP4 container:

• H264
• AAC

MKV container:

• H264
• VP8
• Opus
• AAC
• PCMA
• PCMU
• G722

Multirecorder REST API

REST query must be HTTP/HTTPS POST query like this:

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• streaming.flashphoner.com is WCS server address
• 8081 is a standard WCS REST / HTTP port
• 8444 is a standard WCS REST / HTTPS port
• rest-api is mandatory prefix
• /multipleRecorder/startup is REST method

REST methods and responses

{
 "uri": "multi-recorder://test-record"
}

{
 "uri": "multi-recorder://test-record",
 "mediaSessionId": "866a9910-fbfe-11eb-aae4-6f99b0c80a3a"
}

[
  {
    "mediaSessionsId": [
      "866a9910-fbfe-11eb-aae4-6f99b0c80a3a",
      "9f1e2530-fbfe-11eb-9ec1-77172ac14d86",
      "a970d0a0-fbfe-11eb-8fcc-912807bab442"
    ],
    "uri": "multi-recorder://test-record",
    "fileName": "multi-recorder___test-record.mp4"
  }
]

{
 "uri": "multi-recorder://test-record",
 "mediaSessionId": "866a9910-fbfe-11eb-aae4-6f99b0c80a3a"
}

{
 "uri": "multi-recorder://test-record"
}

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Recording file name

Multiple streams recording file name is formed by template. In this case:

1. {streamName} parameter is set according to recorder URI, replacing all the characters not allowed to use in file system to underline.

Container configuration

The feature is available since build 5.2.1440. By default, multiple recordings are stored to MP4 container

multi_recorder_type=MP4

MKV container may be used if necessary (for example, if VP8+Opus streams are published in conference)

multi_recorder_type=MKV

Recording file name

Multiple streams recording file name is formed by template. In this case:

1. {streamName} parameter is set according to recorder URI, replacing all the characters not allowed to use in file system to underline.

2. {startTime}, {endTime} parameters cannot be set because they depend on stream timestamps, and we have a multiple streams with a different timestamps simultaneously. So it is recommended to use {startTimeMillis}, {endTimeMillis} parameters to add servers clock timestamps to file name.

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A picture sample from the mixed file

Getting tracks information from multiple recording file

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[
  {
    "durationInMS": "78978",
    "trackEdits": [
      {
        "endInMs": "63050",
        "type": "pause",
        "startInMs": "0"
      },
      {
        "endInMs": "78978",
        "type": "media",
        "startInMs": "63050"
      }
    ],
    "channels": "2",
    "trackType": "AUDIO",
    "trackId": "3",
    "timescale": "44100",
    "streamName": "test",
    "trackCodec": "mp4a",
    "sampleRate": "44100",
    "mediaSessionId": "fbbf5b50-20ee-11ec-bf06-ef6ec6048b2c"
  },
  {
    "durationInMS": "39708",
    "trackEdits": [
      {
        "endInMs": "23150",
        "type": "media",
        "startInMs": "0"
      }
    ],
    "channels": "2",
    "trackType": "AUDIO",
    "trackId": "1",
    "timescale": "44100",
    "streamName": "test",
    "trackCodec": "mp4a",
    "sampleRate": "44100",
    "mediaSessionId": "c7bc1460-20ee-11ec-bf06-ef6ec6048b2c"
  },
  {
    "durationInMS": "39791",
    "trackEdits": [
      {
        "endInMs": "23233",
        "type": "media",
        "startInMs": "0"
      }
    ],
    "trackType": "VIDEO",
    "trackId": "0",
    "width": "640",
    "timescale": "90000",
    "streamName": "test",
    "trackCodec": "avc1",
    "mediaSessionId": "c7bc1460-20ee-11ec-bf06-ef6ec6048b2c",
    "height": "360"
  },
  {
    "durationInMS": "63050",
    "trackEdits": [
      {
        "endInMs": "39791",
        "type": "pause",
        "startInMs": "0"
      },
      {
        "endInMs": "50191",
        "type": "media",
        "startInMs": "39791"
      }
    ],
    "trackType": "VIDEO",
    "trackId": "2",
    "width": "640",
    "timescale": "90000",
    "streamName": "test",
    "trackCodec": "avc1",
    "mediaSessionId": "ed3ebda0-20ee-11ec-bf06-ef6ec6048b2c",
    "height": "360"
  }
]

Multiple recording file handling script

When multiple stream recording is finished, a specila handling script is automatically launched as set by the following parameter

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Pulling a separate streams from MKV container

Since build 5.2.1440 a separate streams can be pulled from MKV container using multiple stream mixing tool:

on_multiple_record_hook_script=on_multiple_record_hook.sh

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./offline_mixer_tool.sh

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 --pull-streams ../records/multi-recorder___test-record.mkv

In this case, MKV files will be created per each stream in multirecording:

LOGGER_ENABLED=true

Multithreaded encoding while mixing multiple stream recordings

Since build 5.2.1089 multithreaded encoding can be enabled while mixing multiple stream recordings. To enable this feature, add the following parameter to /usr/local/FlashphonerWebCallServer/conf/offline_mixer.json file

{
  ...,
  "multithreading": true
}

Multiple stream recordings are mixed a twice faster when multithreaded encoding is enabled comparing to singe-threaded one.

Multiple recording data callback

Since build 5.2.1123 it is possible to send PORT query to a certain URL after multiple recording and mixing is finished. This allows to notify backend about file name to which chat room recording is mixed.

Callback URL should be set in /usr/local/FlashphonerWebCallServer/conf/offline_mixer.json file

{
  ...,
  "callbackUrl": "http://backend.url/multiRecorderCallback"
}

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multi-recorder___test-record_fbbf5b50-20ee-11ec-bf06-ef6ec6048b2c.mkv
multi-recorder___test-record_c7bc1460-20ee-11ec-bf06-ef6ec6048b2c.mkv
multi-recorder___test-record_ed3ebda0-20ee-11ec-bf06-ef6ec6048b2c.mkv

If a stream was removed from multirecorder and when added again, or was added a much later then other streams, the gaps will be filled by default to equalize all the pulled streams. This can be disabled if necessary

multi_recorder_mkv_fill_gaps=false

Multiple recording file handling script

When multiple stream recording is finished, a specila handling script is automatically launched as set by the following parameter

on_multiple_record_hook_script=on_multiple_record_hook.sh

By default, script will launch offline_mixer_tool.sh, passing multiple streams recording file name to it.

Since build 5.2.1023, on_multiple_record_hook.sh script writes only file mixing result to log file /usr/local/FlashphonerWebCallServer/logs/multi-record.log, to decrease hard disk I/O load while offline mixing tool is working. A detailed logging mat=y be enabled if necessary by setting the following variable in the script

LOGGER_ENABLED=true

Multithreaded encoding while mixing multiple stream recordings

Since build 5.2.1089 multithreaded encoding can be enabled while mixing multiple stream recordings. To enable this feature, add the following parameter to /usr/local/FlashphonerWebCallServer/bin/on_multiple_record_hook.sh script when launching conf/offline_mixer_tool.sh. Therefore, if  WCS build 5.2.1123 is installed over a previous build, or if custom on_multiple_record_hook.sh is used, the script should be modified as follows:.json file

{
  ...,
  "multithreading": true
}

Multiple stream recordings are mixed a twice faster when multithreaded encoding is enabled comparing to singe-threaded one.

Multiple recording data callback

Since build 5.2.1123 it is possible to send PORT query to a certain URL after multiple recording and mixing is finished. This allows to notify backend about file name to which chat room recording is mixed.

Callback URL should be set in /usr/local/FlashphonerWebCallServer/conf/offline_mixer.json file

# This script copies a recorded stream to client/records
FILE_NAME=$1
CREATION_MODIFICATION_TIME=$2
DURATION_IN_MS=$3
RECORDER_URI=$4
WCS_HOME={
  ...,
  "callbackUrl": "http://backend.url/multiRecorderCallback"
}

A recording data to send are passed via /usr/local/FlashphonerWebCallServer

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/bin/on_multiple_record_hook.sh script when launching offline_mixer_tool.sh. Therefore, if  WCS build 5.2.1123 is installed over a previous build, or if custom on_multiple_record_hook.sh is used, the script should be modified as follows:

# This script copies a recorded stream to client/records
FILE_NAME=$1
CREATION_MODIFICATION_TIME=$2
DURATION_IN_MS=$3
RECORDER_URI=$4
WCS_HOME=/usr/local/FlashphonerWebCallServer
LOG_FILE=$WCS_HOME/logs/multi-record.log
MIXER_TOOL=$WCS_HOME/tools/offline_mixer_tool.sh
# Set LOGGER_ENABLED to true to enable mixing debug logging
LOGGER_ENABLED=false

echo "[$(date '+%Y-%m-%d %H:%M:%S')] Start mixing multiple recording file $FILE_NAME" >> $LOG_FILE

if $LOGGER_ENABLED; then
    bash $MIXER_TOOL $FILE_NAME $CREATION_MODIFICATION_TIME $DURATION_IN_MS $RECORDER_URI >> $LOG_FILE 2>&1
else
    bash $MIXER_TOOL $FILE_NAME $CREATION_MODIFICATION_TIME $DURATION_IN_MS $RECORDER_URI > /dev/null 2>&1
fi

CODE=$?
if [ "$CODE" -ne "0" ]; then
    if [ "$CODE" -eq "64" ]; then
        echo "ERROR: File to mix not found" >> $LOG_FILE
    elif [ "$CODE" -eq "65" ]; then
        echo "ERROR: Offline mixer config not found" >> $LOG_FILE
    else
	    echo "ERROR: Offline mixer tool error code: $CODE" >> $LOG_FILE
	fi
	exit $CODE
fi
echo "[$(date '+%Y-%m-%d %H:%M:%S')] Multiple recording file $FILE_NAME is mixed successfully" >> $LOG_FILE
exit 0

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for RTMP streams with appropriate encoder settings

12. VLC player skips gaps when playing a stream pulled from multirecording in MKV container

Symptoms: gaps in a pulled stream are skipped when playing it in VLC

Solution: use the following parameter

multi_recorder_mkv_fill_gaps=true

13. It is recommended to provide a regular keyframes sending when WebRTC stream is recording to singe MKV file and to MKV multirecorder simultaneously

Symptoms: VLC jumps to time of stream addition to multirecorder when playing a single stream MKV recording

Solution: provide periodic key frames sending for WebRTC streams with the following parameter

periodic_fir_request=true

14. G722 audio can be a shortly distorted when pulling a stream file from MKV multirecording

Symptoms: If the stream with G722 audio was removed and then added again to the multirecorder, a short audio distortions can be heard when the stream was added to multirecorder

Solution: use Opus audio codec

15. PCMA audio may finish earlier than video after stream removing from multirecorder when pulling a stream file from MKV multirecording

Symptoms:  if the stream with PCMA audio was removed from multirecorder, audio finishes earlier than video when playing the pulled stream file

Solution: use Opus audio codec