[FFmpeg-user] Issue with split filter

[Paul B Mahol]

On 1/24/13, Dave Cleal <dmc at vyclone.com> wrote:
> Hi,
>
> I'm trying to use a complex filter to replace severeal existing ffmpeg
> steps with one, to get the job done faster (we do this a lot).
>
> This
>
> ffmpeg -y -i bottom.mp4 -i top.mp4 -i filler.mp4 -filter_complex
> "[2:0]split=4[f1][f2][f3][f4];[0:0]setsar=0:1[video0];
> [f1]select=lt(n\,125)[leader0]; [f2]select=lt(n\,78)[trailer0];
> [leader0][video0][trailer0]concat=n=3[filled0];
> [1:0]setsar=0:1[video1]; [f3]select=lt(n\,0)[leader1];
> [f4]select=lt(n\,45)[trailer1];
> [leader1][video1][trailer1]concat=n=3[filled1];
> [filled0]pad=240:360:0:180 [large]; [large][filled1]
> overlay=0:0,setsar=1:1" -r 30 -b:v 600k -vcodec libx264 looksbad.mp4
>
> does something different to
>
> ffmpeg -y -i bottom.mp4 -i top.mp4 -i filler.mp4 -i filler.mp4 -i
> filler.mp4 -i filler.mp4 -filter_complex "[0:0]setsar=0:1[video0];
> [2:0]select=lt(n\,125)[leader0]; [3:0]select=lt(n\,78)[trailer0];
> [leader0][video0][trailer0]concat=n=3[filled0];
> [1:0]setsar=0:1[video1]; [4:0]select=lt(n\,0)[leader1];
> [5:0]select=lt(n\,45)[trailer1];
> [leader1][video1][trailer1]concat=n=3[filled1];
> [filled0]pad=240:360:0:180 [large]; [large][filled1]
> overlay=0:0,setsar=1:1" -r 30 -b:v 600k -vcodec libx264 looksgood.mp4
>
> As far as I can tell, the only difference between these is that the
> first uses split to get four copies of an input stream, and the second
> just adds it as an input four times. My understanding is that these
> two should be equivalent: is there supposed to be a difference?
>
> It seems that the second does what I expect: the first drops frames,
> freezes here and there, and is 77 frames shorter than I expect it to
> be.
>
> Not too fussed as I do have a workaround, but in some realistic (and
> more complex) examples, I will end up with an awful lot of "-i..."s! So
> it'd be nice to use split if I can.
>
> Thanks in advance for any advice
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