[FFmpeg-user] xfade + acrossfade usage - keeping A/V in sync

[Paul B Mahol]

On 6/17/20, Rob Hallam <ffmpeg at roberthallam.com> wrote:
> On Wed, 17 Jun 2020 at 16:19, Rob Hallam <ffmpeg at roberthallam.com> wrote:
>
>> So it seems that (i) xfade shortens the inputs' combined duration
>> by half the transition duration; (ii) acrossfade does not shorten
>> if there is no overlap (as expected); (iii) acrossfade shortens
>> by the duration of fade if there is overlap.
>
> Pardon the self-reply, but I applied these observations
> to my real-world files and they have consistent A/V
> durations and seem to be in sync. Thanks to Paul for
> the help.
>
> Is it worth documenting this on the wiki, or, not to put too
> fine a point on it: am I the only one who has been initially
> confused by this?

Your offset in xfade is 9 seconds, but it should be 8 seconds.
Because duration of input is 10 seconds and transition duration is 2 seconds.