[Libav-user] Segmenting using pipe

Carl Lindqvist lulebo at gmail.com
Mon Apr 8 18:03:56 CEST 2013

Sorry, wrong list. I will submit my question to ffmpeg-user instead.


2013/4/8 Carl Lindqvist <lulebo at gmail.com>

> Hello
> I have been experimenting with encoding a single file and removing parts
> of the stream. I need this function when encoding material with breaks for
> commercials to remove bars and other funky stuff and sync with the
> subtitles.
> I have done some tests with piping (windows), and I can get this to work
> pretty well for two arbitrary segments as an example:
> (ffmpeg -i inputfile.mp4 -ss 00:10:00 -t 60 -bsf h264_mp4toannexb -vcodec
> copy -acodec copy -f mpegts -
> ffmpeg -i inputfile.mp4 -ss 00:20:00 -t 60 -bsf h264_mp4toannexb -vcodec
> copy -acodec copy -f mpegts - )| ffmpeg -y -f mpegts -i - -c:v libx264
> -preset veryfast -x264opts keyint=75:min-keyint=75:no-scenecut -b:v 704k
> -minrate 704k -maxrate 704k -bufsize 1500k -profile:v baseline -aspect 16:9
> -c:a libvo_aacenc -b:a 96k -ac 2 test.mp4
> (this will create a two minute file from two different sections of the
> input file)
> The problem is the codec copying in the first parts. Since the timecodes
> might begin in the middle of a GOP, the final ffmpeg will not know what to
> do until the first I-frame shows up, so it just shows a freeze frame until
> that happens.
> There is a requirement of a fixed gop size of 3 secs for the final output
> file, so I need to do the encoding again for the final step, no cat can be
> used on segments.
> Is there a good intermediate codec to decode to in the first step?
> (Preferrably uncompressed to gain performance) I have found yuv4mpegvideo
> but that only does video. I need the audio as well. Anyone got any smart
> ideas?
> /Carl
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