如何将Firefox连接到Chrome以通过WebRTC传输h264？

Question

I try to connect Firefox 45 to Chrome 51dev to transfer h264 video. Firefox to Firefox and Chrome to Chrome works perfectly. But Firefox to Chrome transfers vp8 video even though I set the priority h264.

To set the codec priority I used this link: https://miguelpdl.github.io/WebRTC-codelab/session06/lab/html/step03.html

On the answer side remote description contains:

m=video 53100 UDP/TLS/RTP/SAVPF 107 100 101 116 117 96 97 99 98
...
a=rtpmap:107 H264/90000
a=rtpmap:100 VP8/90000
a=rtpmap:101 VP9/90000
a=rtpmap:116 red/90000
a=rtpmap:117 ulpfec/90000
a=rtpmap:96 rtx/90000
a=rtpmap:97 rtx/90000
a=rtpmap:99 rtx/90000
a=rtpmap:98 rtx/90000

But local description contains only:

m=video 9 UDP/TLS/RTP/SAVPF 100
...
a=rtpmap:100 VP8/90000

Can I connect Firefox to Chrome to transfer h264?

Answer 1

Chrome does not yet support H.264. For proof, see this fiddle which removes the VP8 codec.

The fiddle lets you cut'n'paste offer/answers to make a connection between two tabs or browsers, but for now, just paste the offer into a text editor and look at it:

You'll find that Firefox offers H.264 to spec:

a=rtpmap:126 H264/90000
a=rtpmap:97 H264/90000    

whereas Chrome offers VP8 only, in spite of us just having removed it:

a=rtpmap:100 VP8/90000

So when you say it works from Chrome to Chrome, I think you're really seeing VP8.

They are apparently working H.264 though.

Update: Apparently H.264 support is behind a flag in Chrome 50 . Enable it with:

chrome://flags/#enable-webrtc-h264-with-openh264-ffmpeg