Concat filter not working

[Marth64]

Summary of the bug:
Concat filter on multiple inputs (same file or different file) not working combined with -ss/-to after multithreading upgrade. Output EOFs after the first segment, and concatenation isn't actually happening. This is a relatively simple filter expression that should work IMO. A user from IRC support reported it, and I was able to successfully reproduce it.

I traced this to commit d35c05cb9ee39e1d90fab326a6aaec6c6c9433e1 (fftools/ffmpeg_filter: move filtering to a separate thread)

Command to reproduce: 

How to reproduce:

ffmpeg  -ss 0 -to 2 -i ~/Desktop/in1.mkv  -ss 2  -to 4 -i ~/Desktop/in2.mkv -filter_complex "[0:v:0][0:a:0][1:v:0][1:a:0]concat=n=2:v=1:a=1[concat_v][concat_a]" -map '[concat_v]' -map '[concat_a]' test.mp4

Expected outcome: Segment 1 + Segment 2 (4s).
Actual outcome: only Segment 1 (2s).

[Gyan]

Reproduced. This bug is not contingent on using -ss/-to/-t

It can be reproduced with

ffmpeg -i in1.mkv -i in2.mkv 
-filter_complex
 "[0:v:0]trim=0:2[v0];[0:a:0]atrim=0:2[a0];
  [1:v:0]trim=2:4,setpts=PTS-STARTPTS[v1];[1:a:0]atrim=2:4,asetpts=PTS-STARTPTS[a1];
  [v0][a0][v1][a1]concat=n=2:v=1:a=1[concat_v][concat_a]"
-map '[concat_v]' -map '[concat_a]' test.mp4

[elenril]

Should be fixed in 1ea2e757f7cba714eefd27efb2f9285078bba4a3