Webrtcbin + h264, depayload > parse > payload yields different profile-level-ids

[Trey Hutcheson]

And this may be an issue elsewhere. It looks like it's not the
profile-level-id. It may be some sdp munging downstream. I'll update as
soon as I confirm

On Tue, Feb 16, 2021 at 9:00 AM Trey Hutcheson <trey.hutcheson at gmail.com>
wrote:

> Here's the situation:
> Peer 1 > media server (gstreamer) > Peer 2
> * Peer 1 creates an offer that contains h264.
> * When the media arrives and webrtcbin fires the pad-added signal, the
> media server "repayloads" the stream (queue ! rtph264depay ! h264parse
> config-interval=-1 ! rtph264pay pt={}), and connects to another webrtcbin
> instance, and creates a new offer
> * the offer is presented to the second remote peer, and ultimately
> rejected, because it doesn't understand the profile-level-id
>
> This is in chrome, but I've seen the same behavior with safari (though the
> profiles are different).
>
> Original video offer sdp fragment:
> a=rtpmap:102 H264/90000
> a=rtcp-fb:102 goog-remb
> a=rtcp-fb:102 transport-cc
> a=rtcp-fb:102 ccm fir
> a=rtcp-fb:102 nack
> a=rtcp-fb:102 nack pli
> a=fmtp:102
> level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42001f
>
> Caps observed on the pad-added signal:
> Caps("application/x-rtp, media=(string)video, payload=(int)102,
> clock-rate=(int)90000, encoding-name=(string)H264,
> profile-level-id=(string)42001f, level-asymmetry-allowed=(string)1,
> packetization-mode=(string)1, rtcp-fb-nack-pli=(boolean)true,
> rtcp-fb-ccm-fir=(boolean)true, ssrc=(uint)4118433928")
>
> 2nd offer created by webrtcbin, after "repayloading" the stream:
> a=rtpmap:102 H264/90000
> a=rtcp-fb:102 nack pli
> a=fmtp:102
> profile-level-id=42c015;packetization-mode=1sprop-parameter-sets=Z0LAFYyNQKD5APCIRqA=,aM48gA==
>
> And outbound caps:
> Caps("application/x-rtp, media=(string)video, clock-rate=(int)90000,
> encoding-name=(string)H264, packetization-mode=(string)1,
> profile-level-id=(string)42c015,
> sprop-parameter-sets=(string)\"Z0LAFYyNQKD5APCIRqA\\=\\,aM48gA\\=\\=\",
> payload=(int)102, ssrc=(uint)1172136079, timestamp-offset=(uint)1112621284,
> seqnum-offset=(uint)402")
>
> Notice the original profile-level-id was 42001f, but the new
> profile-level-id was 42c015
>
> In the case of safari (M1 mac mini) on both ends, the original profile
> level id was 640c1f, but the repayloaded profile-level-id was 64001f
>
>
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