fn h264_sps(stream: &[u8]) -> Option<(u32, u32, u32)>
(log2_max_frame_num, max_num_ref_frames, chroma_format_idc) of the first SPS in an Annex-B H.264 stream.
(log2_max_frame_num, max_num_ref_frames, chroma_format_idc)