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

[Rob Hallam]

On Tue, 16 Jun 2020 at 23:56, Paul B Mahol <onemda at gmail.com> wrote:

>> TR1=764.3    # input 0 duration - 1 second
>> TR2=1250.498    # input 0 + input 1 duration - 1 second

> I believe this two should be - 2 seconds instead. Because both
> transition durations for two xfade and acrossfade filters is 2
> seconds.

Thanks for the reply Paul, I will try that.

My reading of xfade is that the transition start point should be
half the duration from the end- the example on the wiki is 4.5s
of a 5s input for a 1s transition. I am less sure about acrossfade,
but thought it worked similarly.

In either case diagram terms I figured they operated like:

[AA AA AA AA][BB BB BB BB]
↓
[AA AA AA AB BA BB BB BB]

ie neither should change the length of the inputs they operate on.

Is that a mistaken assumption perhaps?

Cheers,
Rob