Return the next frame of a stream.
This function returns what is stored in the file, and does not validate
that what is there are valid frames for the decoder. It will split what is
stored in the file into frames and return one for each call. It will not
omit invalid data between valid frames so as to give the decoder the maximum
information possible for decoding.
If pkt->buf is NULL, then the packet is valid until the next
av_read_frame() or until avformat_close_input(). Otherwise the packet
is valid indefinitely. In both cases the packet must be freed with
av_packet_unref when it is no longer needed. For video, the packet contains
exactly one frame. For audio, it contains an integer number of frames if each
frame has a known fixed size (e.g. PCM or ADPCM data). If the audio frames
have a variable size (e.g. MPEG audio), then it contains one frame.
pkt->pts, pkt->dts and pkt->duration are always set to correct
values in AVStream.time_base units (and guessed if the format cannot
provide them). pkt->pts can be AV_NOPTS_VALUE if the video format
has B-frames, so it is better to rely on pkt->dts if you do not
decompress the payload.
Return the next frame of a stream. This function returns what is stored in the file, and does not validate that what is there are valid frames for the decoder. It will split what is stored in the file into frames and return one for each call. It will not omit invalid data between valid frames so as to give the decoder the maximum information possible for decoding.
If pkt->buf is NULL, then the packet is valid until the next av_read_frame() or until avformat_close_input(). Otherwise the packet is valid indefinitely. In both cases the packet must be freed with av_packet_unref when it is no longer needed. For video, the packet contains exactly one frame. For audio, it contains an integer number of frames if each frame has a known fixed size (e.g. PCM or ADPCM data). If the audio frames have a variable size (e.g. MPEG audio), then it contains one frame.
pkt->pts, pkt->dts and pkt->duration are always set to correct values in AVStream.time_base units (and guessed if the format cannot provide them). pkt->pts can be AV_NOPTS_VALUE if the video format has B-frames, so it is better to rely on pkt->dts if you do not decompress the payload.
@return 0 if OK, < 0 on error or end of file