- demuxing: either set by the user before avformat_open_input() (then
the user must close it manually) or set by avformat_open_input().
- muxing: set by the user before avformat_write_header(). The caller must
take care of closing / freeing the IO context.
Do NOT set this field if AVFMT_NOFILE flag is set in
iformat/oformat.flags. In such a case, the (de)muxer will handle
I/O in some other way and this field will be NULL.
I/O context.
- demuxing: either set by the user before avformat_open_input() (then the user must close it manually) or set by avformat_open_input(). - muxing: set by the user before avformat_write_header(). The caller must take care of closing / freeing the IO context.
Do NOT set this field if AVFMT_NOFILE flag is set in iformat/oformat.flags. In such a case, the (de)muxer will handle I/O in some other way and this field will be NULL.