concat of videos with different frame rates ends with endless loop of frame duplication

[rotemc]

Summary of the bug:

---

It seems that concatenation command for videos with different frame rates gets into endless loop of duplicating frames.

Debug tracing for example:

---

cur_dts is invalid st:0 (0) [init:1 i_done:0 finish:0] (this is harmless if it occurs once at the start per stream)

Last message repeated 2 times

* 33331 dup!
More than 1000 frames duplicated

It works fine in 4.2

How to reproduce:

---

% /opt/ffmpeg-4.4.1/bin/ffmpeg -loglevel debug -y -timelimit 2880 -i spec/videos/first.mp4 -i spec/videos/second.mp4 -sws_flags lanczos -filter_complex "[0:v]null[j1] ; [0:a]anull[a1] ; [1:v]null[j2] ; [1:a]anull[a2] ; [j1][a1][j2][a2]concat=n=2:a=1:v=1[v9][a3]" -codec:v libx264 -map '[v9]' -map '[a3]' -start_at_zero public/test.mp4
ffmpeg version 4.4.1
built on Ubuntu/mac

[rotemc]

use file with the given command