Read one packet and put it in 'pkt'. pts and flags are also
set. 'avformat_new_stream' can be called only if the flag
AVFMTCTX_NOHEADER is used and only in the calling thread (not in a
background thread).
@return 0 on success, < 0 on error.
When returning an error, pkt must not have been allocated
or must be freed before returning
Read one packet and put it in 'pkt'. pts and flags are also set. 'avformat_new_stream' can be called only if the flag AVFMTCTX_NOHEADER is used and only in the calling thread (not in a background thread). @return 0 on success, < 0 on error. When returning an error, pkt must not have been allocated or must be freed before returning