Implement recording to Matroska files.
The format to use is determined by the option -F/--record-format if set,
or by the file extension (".mp4" or ".mkv").
Some containers force their own time base. For example, matroska
overwrite time_base to (AVRational) {1, 1000}.
Therefore, rescale our packet timestamps to the output stream time base.
Suggested-by: Steve Lhomme <robux4@ycbcr.xyz>
AVStream.codec has been deprecated in favor of AVStream.codecpar.
Due to the FFmpeg/Libav split, this happened in two separate versions:
- 57.33.100 for FFmpeg
- 57.5.0 for Libav
