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Re: What does a track contain?

From: Martin Thomson <martin.thomson@gmail.com>
Date: Wed, 2 Mar 2016 13:11:35 +1100
Message-ID: <CABkgnnVCzrZe7ygPukf11ytmoFvPgMoYXYPNGcfgK7_MgmLQEQ@mail.gmail.com>
To: Harald Alvestrand <harald@alvestrand.no>
Cc: "public-media-capture@w3.org" <public-media-capture@w3.org>
That seems like the obvious answer to me.  Now, what to *do* about it.

On 29 February 2016 at 22:31, Harald Alvestrand <harald@alvestrand.no> wrote:
> I think we should expect the sequence
>
> <alpha-supporting canvas> -> mediaStreamTrack -> <video>
>
> to deliver the alpha channel. Anything else seems like a bug.
>
> But I think we have to admit that
>
> <alpha-supporting canvas> -> mediaStreamTrack -> PeerConnection -> H.264
> baseline encoding -> PeerConnection -> MediaStreamTrack -> <video>
>
> is going to lose the alpha channel. We can play tricks with VP8, and I
> think there exist H.264 extensions with alpha support too, but there are
> times we're going to lose it.
>
> I think that just has to be documented in webrtc-pc: "Encode what you can".
>
>
>
> Den 24. feb. 2016 19:34, skrev Peter Thatcher:
>> FYI, someone answered my question with this:
>>
>> http://simpl.info/videoalpha/
>>
>> Works in Chrome, but not Firefox.
>>
>> On Wed, Feb 24, 2016 at 8:28 AM, Peter Thatcher <pthatcher@google.com
>> <mailto:pthatcher@google.com>> wrote:
>>
>>     I don't know enough about <video> to know the answer to this:  if it
>>     has an alpha channel in it, and it's rendered on top of other web
>>     elements, is it supposed to render such that you potentially see
>>     through the video to the other web elements below?  In other words,
>>     could I use a <video> to make a video of a translucent ghost fly
>>     around a web page?  Is that the kind of thing we're going for here?
>>       canvas -> track -> <video> -> ghost?
>>
>>     On Wed, Feb 24, 2016 at 8:20 AM, Martin Thomson
>>     <martin.thomson@gmail.com <mailto:martin.thomson@gmail.com>> wrote:
>>
>>         On 24 February 2016 at 08:13, Peter Thatcher
>>         <pthatcher@google.com <mailto:pthatcher@google.com>> wrote:
>>         > What do you mean "throughout the media pipeline"?  Do you expect a track
>>         > sent through a PeerConnection to have the alpha channel intact when it comes
>>         > out the remote side?
>>
>>         Well, we know that RTP video is generally incapable of handling
>>         alpha
>>         channels, so no.  Unless and until we find a codec that supports an
>>         alpha channel (APNG perhaps).
>>
>>         But the simple example of <canvas> piped to <video> presents
>>         something
>>         of a challenge.
>>
>>
>>
>
Received on Wednesday, 2 March 2016 02:12:07 UTC

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