I'm trying to write a decoder for a webrtc app in C. I receive a RTP stream, I parse every packet, reorder them, and put the payload in a AVPacket, as described here (FFmpeg decode raw buffer with avcodec_decode_video2). The reordering part is not described in this link but I'm pretty sure this part is OK.
The question is, I dont know how to give the decoder information about resolution, pix_fmt etc. Do I need to create an AVstream* and fill it with all information I took from rtp header?
Do someone have a piece of running code that decode a VP8 packet depacketized without the use of rtp_dec etc.?
In this link, no more information seems to be sent to the decoder, is it able to decode without knowing resolution and without any header?
You don't need to feed "resolution, pix_fmt etc." information to decoder, as those get derived by decoder from the input AVPackets.
Encoders need such information like resolution, pix_fmt etc. to generate the compressed byte/bit-stream. And, encoders embed this (resolution, pix_fmt etc.) information in generated bit-stream. Once decoder receives bit-stream in right order, it derives the resolution, pix_fmt info before proceeding to de-compressing it.
Probably, the packet order that you are feeding to decoder is the cause in your case.