Yikes!!!! In the example script please change: color=blue, trim=0:3 [blue];
to be 5 seconds long (trim=0:5), then follow along with the text below. SORRY! On Thu, Sep 30, 2021 at 11:57 AM Arif Driessen <arif...@gmail.com> wrote: > Consider this script: > > --- > #!/bin/bash > > ffmpeg \ > -v error \ > -filter_complex \ > " > color=blue, > trim=0:3 > [blue]; > > color=red, > trim=0:5 > [red]; > > [blue][red] > xfade > " \ > -vcodec libx264 \ > -f matroska out.mkv && \ > ffprobe -v error \ > -select_streams v \ > -of csv=print_section=0 \ > -show_entries format=duration \ > out.mkv > > exit 0 > --- > > It will report the duration of the resultant mkv file is 5 seconds. > Intuition would tell me to expect it to be 10 seconds long. > > Change the duration of [blue] to 3 seconds, and the resultant duration is > still 5 seconds. Aha! So xfade blends the first input INTO the second. I > don't believe the documentation is clear on this: > > > Apply cross fade from one input video stream to another input video > stream. The cross fade is applied for specified duration > > Out of curiosity, what would happen if we keep the duration of [blue] to > 3, but set the xfade=offset to 2 seconds, since xfade=duration by default > is 1... Now the resultant mkv file is 7 seconds long!? Can you explain the > rationale? > > Even weirder, now let's set the duration of [blue] to 3 seconds and make > xfade=offset 3 seconds also... Now the resultant mkv file is 3 seconds > long!! Is this just undefined behaviour because we have attempted illegal > behaviour? (offset + duration >= input_duration) > > Should we update the documentation to be clearer on this? (I am happy to > do the work). It was the source of a frustating timing issue that took me > all day to resolve. (back when I was emailing here about concating and > fading sources). > > Btw, acrossfade, works intuitively, and thus (for me) without fault. This > concern/ambiguity is also expressed in Michael Koch's FFmpeg book. > > Thanks, > Arif Driessen > > _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
