mux: extradata: add support H264 and HEVC
Use hxxx_helper to extract the SPS/PPS/VPS payload from the stream and report it when it has been found.
It adds support for late-signalling of h264 and hevc codec specific data to the mp4 mux, after pf_add has been called, which is needed for some asynchronous encoders like VideoToolbox and MediaCodec that won't report the format until they can also output the first I-frame, which means after encoder_t::ops::encode_video has been called at least once.
Edited by Alexandre Janniaux