[Libav-user] Doubts in ffmpeg

Mayank Agarwal mayank77fromindia at gmail.com
Mon Jan 13 13:31:50 CET 2014


I am trying to understand mp4 file and ts demuxing/decoding and has
following doubts.Please help me clarify.


i have the following doubts in ffmpeg.Please clarify

1.I am reading mp4 file using ffmpeg and after doing av_read_frame
i am getting video(stream_index = 0),audio(stream_index = 1) packets
First there is no order of coming of video/audio packets.Is it the standard

2.Video pgackets are coming of various sizes from the minimum of 14 to the
maximum of 21824.Please point why the video packet size varies,somewhere it
is written that for video one packet means one frame,so if for video
pkt->size = 14 also equals one frame of video.(pkt is of type AVPacket).

3.If we demux the incoming mp4 stream in Probe function while parsing it
and store the info in some buffer or calling av_read_frame demuxes it.

4.Is it possible in ffmpeg to demux the mp4 file and then assign both a/v
in one stream of packets where video packet has stream_index = 1,and for
audio = 0.
or it has to be in separate stream.

5.Diff between ffmpeg processing for transport stream and mp4 file.
if both are demuxed,decoded in same way or is it different.

6.Please point me any example to add subtitle to the mp4 file in ffmpeg.

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