DNG - aspect ratio suddely changes mid-clip

[Eugene]

Summary of the bug:

In a DNG (image2) -> H.264 (libx264) transcode, the output aspect ratio and frame alignment suddenly changes around frame 12

First 12 frames (as expected, but off color):

Frames 13 onwards (layout distorted):

How to reproduce:

Simple repro (25 frames, all identical): ​https://www.dropbox.com/s/556rltwsukogc4q/ffmpeg-repro.tgz?dl=0

ffmpeg -stats -f image2 -start_number 0 -i D001_C001_20200907_R0%04d.dng -f mp4 -vcodec libx264 -y -s 1280x720 -pix_fmt yuv420p out.mp4

Tested with ffmpeg 4.2, 4.4 and 4.5-dev (git-2021-03-20-c361fa9), also the same result with a different output encoder and format.

[Michael Koch]

I can reproduce the problem.

[Balling]

(as expected, but off color):

And why is that? P.S. Ah, right that is issue #7367, see its comments. Sigh.

[Carl Eugen Hoyos]

Reproducible for example with this command line:

$ ffmpeg -loop 1 -i D001_C001_20200907_R00000.dng -f image2 -update 1 -vcodec rawvideo md5: