support for alpha channel when transferring canvas.

[jimmywarting]

RTCPeerConnection does not seem to support the alpha channel. is there any trick into choosing a encoder / codec that supports alpha channel also?

the video i'm capturing is coming from a canvas.captureStream() and it dose not have a background. and the receiver instead sees a solid black background.

it's evident on demos such as:

• https://webrtc.github.io/samples/src/content/capture/canvas-pc/
• https://stackoverflow.com/a/58341171/1008999

it's unfortunately that we have to resort to solutions such as: https://github.com/webrtcHacks/transparent-virtual-background

there should be a way with webrtc to transfer video with alpha channels

[fippo]

Support for alpha channel (or lack thereof) is a long standing issue (as you found out in the samples repository)

https://bugs.chromium.org/p/chromium/issues/detail?id=1395218 is the most recent incarnation in Chrome, maybe @rosetta-jpn knows whether it is supposed to work.

[rosetta-jpn]

@jimmywarting Could you file an issue in Chromium (https://crbug.com) ccing folks in the above metioned issue tracker? This is not what I can make a decision on my own. We have been alive in the manner of dropping alpha channel in RTCPeerConnection for a long time for the sake of better performance. Changing it needs the disucission.

Thanks!

[rosetta-jpn]

By the way, does the Firefox work in the same manner?

[jimmywarting]

By the way, does the Firefox work in the same manner?

Firefox and safari both also display black backgrounds