[FFmpeg-user] What am I doing wrong with xfade

[Cecil Westerhof]

Paul B Mahol <onemda at gmail.com> writes:

> On 9/10/22, Cecil Westerhof via ffmpeg-user <ffmpeg-user at ffmpeg.org> wrote:
>> I have to concatenate about 30 videos together with xfade. Because I
>> did not mange to find a way to do that in one command I wrote a script
>> that does 1 and 2 to 1-2, 3 and 4 to 3-4, 4 and 5 to 5-6, …
>> Then 1-2 and 3-4 to 1-4, 5-6 and 7-8 to 5-8, …
>> Etcetera.
>>
>> But it seems that in every iteration the audio goes out of sync with
>> about one second.
>>
>> Example of one of the commands:
>>     nice -n 10 ionice -c3 time ffmpeg -y \
>>       -i snellerDanDeWind.mkv            \
>>       -i deFinale.mkv                    \
>>       -vcodec libx264                    \
>>       -crf 26                            \
>>       -acodec libmp3lame                 \
>>       -qscale:a 9                        \
>>       -preset veryfast                   \
>>       -filter_complex
>>     'xfade=transition=slidedown:duration=4:offset=126.083000;acrossfade=d=4'
>> \
>
> Offset should be first video duration minus xfade duration.
> Assuming that audio is not longer than video.

>>           DURATION        : 00:02:10.083000000

But that is the case.
02:10.083000000 -> 130.083
130.083 - 4 = 126.083

Audio and video off the first file are the same.
Strangely the video of the second file is 0.44 seconds longer as the
audio. But that should not be a problem?

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof