[FFmpeg-user] Use concat filter with a fade

[Michael Koch]

Am 14.06.2022 um 15:33 schrieb Cecil Westerhof via ffmpeg-user:
> Michael Koch <astroelectronic at t-online.de> writes:
>
>> Am 14.06.2022 um 13:47 schrieb Cecil Westerhof via ffmpeg-user:
>>> Sometimes I have to cut parts out of a video. I now use for this (bash on Debian):
>>>       ffmpeg -y                                                \
>>>              -ss ${videoStart} -to ${cutStart} -i ${inputFile} \
>>>              -ss ${cutEnd}     -to ${videoEnd} -i ${inputFile} \
>>>              -vcodec         libx264                           \
>>>              -crf            26                                \
>>>              -acodec         libmp3lame -qscale:a 9            \
>>>              -preset         veryfast                          \
>>>              -lavfi "concat=n=2:v=1:a=1"                       \
>>>              -an ${outputFile}
>>>
>>> But the cut from one part to another is a bit abrupt. Is there a
>>> possibility to smooth it with something like a fade?
>> you can use the xfade filter. :
>> https://www.ffmpeg.org/ffmpeg-all.html#xfade
>> https://trac.ffmpeg.org/wiki/Xfade
> I am now using:
>      offset=$((${cutStart} - ${videoStart} - ${duration}))
>      xfade=xfade=transition=slideleft:duration=${duration}:offset=${offset}
>      time ffmpeg -y                                             \
>            -ss ${videoStart} -to ${cutStart} -i ${inputFile}    \
>            -ss ${cutEnd}     -to ${videoEnd} -i ${inputFile}    \
>            -vcodec         libx264                              \
>            -crf            26                                   \
>            -acodec         libmp3lame -qscale:a 9               \
>            -preset         veryfast                             \
>            -filter_complex ${xfade}                             \
>            ${outputFile}
>
> But I have a major and minor problem.
> The major problem is that I do not have audio from the second part of
> the video.

Audio has its own filter: acrossfade

> The minor problem is that I have to calculate the offset. It would be
> nice if I could use -duration, but that does not work sadly.

As far as I know this isn't yet implemented.

> By the way: how should I do it when I want to use five parts of the video?

I haven't tested this, but I think you must build a binary tree:
[0:v][1:v]xfade[a];[2:v][3:v]xfade[b];[a][b]xfade

Michael