Stream watermarking¶

Overview¶

A watermark can be applied to stream captured while translating it to subscribers. To do this, the following parameter should be added to flashphoner.properties file to specify watermark PNG file name:

custom_watermark_filename=watermark.png

Watermark PNG file should be placed to /usr/local/FlashphonerWebCallServer/conf catalog.

Watermark can be added only using the commercial license because Flashphoner watermark will be added to all streams when trial license is used.

If watermark picture contains black regions, those regions will not be displayed because black is background color for video playback.

Stream transcoding must be enabled to add watermark, because stream must be decoded and then encoded with picture applied for further broadcasting. To enable transcoding, the stream resolution can be set explicitly when publishing

session.createStream({name:'stream1',constraints:{audio:true,video:{width:640,height:480}}}).publish();

and playing the stream

session.createStream({name:'stream1',constraints:{audio:true,video:{width:320,height:240}}}).play();

In this case all the streams are publishing on server in 640x480 resolution and are playing in 320x240. That automatically enables transcoding, rescaling from 640x480 to 320x240 and watermark applying.

Stream watermarking will increase the server load approximately 0.5-1 core for each incoming video stream depending on video transcoded resolution. For example, 16 incoming streams handling may require 8-16 core server. In this regard, it is recommended to apply watermark on stream publisher source if possible.

Watermark picture mixing with alpha channels support¶

Some watermark picture colors may be distorted or invisible (transparent) when applying this picture as watermark. It depends on alpha channel values of the picture applied. Since build 5.2.1064 the following parameter is added to enable watermark picture mixing with alpha channels support

custom_watermark_mix=true

Note that alpha channels support implementation today executes a many subsequental operations. This can lead to CPU load inscreasing and low quality of the resulting image. In the future, it is planned to be implemented using parallel mixing on GPU.

Watermark picture downloading from external site¶

Since build 5.2.2087 a watermark picture may be downloaded from external site by URL

custom_watermark_filename=https://server/pics/watermark.png

There will be black picture in output stream if server is not available, or the file is not found on the server with a corresponding error message in server log

09:41:01,342 WARN       CustomWatermark - API-ASYNC-pool-7-thread-3 Can't read custom watermark file - https://server/pics/watermark.png
java.net.ConnectException: Connection refused (Connection refused)

or

09:43:36,235 WARN       CustomWatermark - API-ASYNC-pool-7-thread-3 Can't read custom watermark file - https://server/pics/watermark.png
java.io.FileNotFoundException: https://server/pics/watermark.png

Known issues¶

1. Default watermark (black picture) will be used if is damaged or absent¶

Symptoms

Black picture in output stream when watermark is added, there is a message in server log

Wrong watermark file format. Should be PNG.

Solution

Use only correct PNG file to add watermark