[FFmpeg-user] Dropping frames on simple split and recombine.

[Moritz Barsnick]

Hi Scott,

On Tue, Sep 15, 2015 at 07:44:35 -0500, Scott Chamberlain wrote:
> And my output video freezes the top timer at 7:03 like before and the
> bottom timer now freezes at 4:29. (See Out1.mp4)

I think it's vstack that has issues at 02:03, consistently. I reduced
your filter to (split and vstack without concat):

"select='1+gt(t,5)+gt(t,10)':n=3[v1][v2][v3];[v1]setpts=PTS-STARTPTS[v1o];[v2]setpts=PTS-STARTPTS[v2o];[v3]setpts=PTS-STARTPTS[v3o];[v1o][v2o][v3o]vstack=3"

And it exposes the same overflow and stall. Even if you reduce to two:

"select='1+gt(t,7.5)':n=2[v1][v2];[v1]setpts=PTS-STARTPTS[v1o];[v2]setpts=PTS-STARTPTS[v2o];[v1o][v2o]vstack=2"

If you add -ss as an input option, the stalling behavior will just
shift.

Using "-t" as an input option, it becomes apparent that the vstack
buffer queue overflow appears between 2.1 and 2.2 seconds, so it
obviously correlates with the stall. (I checked this just in case.)

Now, I managed to get it to work by inserting the fifo before [v1o]:

"select='1+gt(t,7.5)':n=2[v1][v2];[v1]setpts=PTS-STARTPTS,fifo[v1o];[v2]setpts=PTS-STARTPTS[v2o];[v1o][v2o]vstack=2"

Unfortunately, that doesn't help in your original filter chain. But
good luck experimenting from here. ;-)

Moritz