[FFmpeg-user] Apply format with overlay and -ss in front of inputfile is strange?

[nicolab]

>Nicolas George <george <at> nsup.org> writes:
>
>> Le quintidi 25 messidor, an CCXXIII, Carl Eugen Hoyos a écrit :
>> > I can confirm that there may be an issue
>> > but it is not overlay-related:
>> > $ ffmpeg -i input -vf
>> > "split[x][z];[x]format=gray[x1];[x1]nullsink"
>> > -strict -2 -vcodec jpeg2000 -ss 1 out1.avi
>> >
>> > $ ffmpeg -ss 1 -i input -vf
>> > "split[x][z];[x]format=gray[x1];[x1]nullsink"
>> > -strict -2 -vcodec jpeg2000 out2.avi
>>
>> If the issue is that the output is converted to
>> gray too, then this is the expected behaviour.
>
>In the first case (without "seeking") one "stream"
>(this is not the right term I fear) is converted
>the other one is left unchanged.
>In the second case (with seeking) both streams
>are converted to gray.
>
>While I understand that the filterchain may not
>be unambiguous, it looks identical in both cases.
>
>Note that the following command produces gray
>output in yuv420p, it appears that two scale
>filters instead of the optimal one filter is
>inserted:
>$ ffmpeg -ss 1 -i input -vf
>"split[x][z];[x]format=gray[x1];[z]format=yuv420p;[x1]nullsink"
>-strict -2 -vcodec jpeg2000 out2.avi
>
>> For the rare cases where it does matter, for
>> example to be sure to deinterlace before
>> converting, you need to insert the scale filter
>> explicitly at the point you want the format
>> conversion.
>
>Which is in front of the format filter iiuc.
>
>> In this particular case, my guess is that
>> libavfilter decided to insert the scale filter
>> before split. Insert explicitly after split
>> and it should work as expected.
>
>It does, yes. 

Thank you for the explanation, Carl Eugen and
Thank you for the additional explanation, Nicolas George



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