CODEWITHSUNDEEP
webrtch.264libdatachannel
Kostya Vasilyev
Kostya Vasilyev

Reputation: 73

WebRTC - receiving H264 key frames

I've been playing with WebRTC using libdatachannel, experimenting and learning.

Wrote some code to parse RTP packets into NALU's, and testing connecting to a "known good" server which sends H264 video.

Problem:

I'm only seeing NALU's with type = 1 (fragmented into multiple FU-A's) and sometimes type = 24 (which contain embedded SPS and PPS NALU's).

So I don't understand how to decode / render this stream - I would expect the server to send a NALU with a key frame (NALU type 5) automatically to a newly connected client, but it does not.

What am I missing to be able to decode the stream? What should I do to receive a key frame quickly? If my understanding is correct, I need a key frame to start decoding / rendering.

Tried requesting a key frame from code - it does arrive (type 5) but after some delay which is undesirable.

And yet the stream plays perfectly fine with a web browser client (Chrome, JavaScript) and starts up quickly.

Am I maybe overthinking this, and the browser also has a delay but I'm just perceiving it as instant?

In any case, what's the situation with key frames? Is a client supposed to request them (and without that, a server should not be expected to send them)?

If so what's a good interval? One second, two, three?

Upvotes: 0

Views: 1096

Answers (0)

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