[FFmpeg-user] ffmpeg architecture question

[Paul B Mahol]

On 4/21/20, Michael Koch <astroelectronic at t-online.de> wrote:
>
>>> I now appreciate that 'blend' has a "preferred" input similar to
>>> 'overlay',
>>> but that behavior is not
>>> documented. In the case of 'overlay', the name "main" doesn't convey that
>>> meaning, and in the case
>>> of 'blend', that behavior is not documented at all. Both documentations
>>> should explain how
>>> timestamps control output and that the 1st filter-input's timestamp
>>> determines the filter-output's
>>> timestamp.
>> Blend filter does not have preferred input since long time.
>
> If the blend filter gets two input frames with different timestamps,
> then what's the timestamp of the output frame?
> I can think ot at least 5 possible scenarios:
> -- timestamp is copied from the first input
> -- copied from the second input
> -- the smaller of the two timestamps
> -- the larger of the two timestams
> -- the artihmetic mean of the two timestamps
>

It is discouraged to use blend in such case.
Inputs must have same timestamps anyway I you wish to do anything useful.
Also timebase is picked from framesync.