[FFmpeg-trac] #11374(undetermined:new): Deprecated -fflags shortest option may still be useful

[FFmpeg]

#11374: Deprecated -fflags shortest option may still be useful
-------------------------------------+-------------------------------------
             Reporter:  Wallboy      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:  concat       |               Blocked By:
  concatenate demuxer shortest       |
  timestamp dts                      |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 '''Summary of the bug:'''

 I use ffmpeg and the concat demuxer to concatenate multiple mp4 files
 together, but was having issues with `"Application provided invalid, non
 monotonically increasing dts to muxer"` errors that would occur when the
 next file was opened.

 I was able to solve this error in almost all cases by pre-processing the
 input files by simply doing a streamcopy and specifying `-fflags
 +shortest`. I also tried using `-shortest`, but this would still result in
 the timestamp errors.

 I noticed the warning message that the `-fflags shortest` option is
 deprecated and will be removed at some point in the future. I can see the
 commit for deprecation here:
 https://github.com/FFmpeg/FFmpeg/commit/85e075587dcca5e07c89b5c2f1081d773ce4d997
 which seems to imply it's being removed because it was assumed it was
 never used practically anywhere, or what bugs it actually solved.

 '''How to reproduce:'''

 I have provided three sample test files: `test_no_shortest.mp4`,
 `test_shortest.mp4`, and `test_mux_shortest.mp4` which were all created
 with the following three ffmpeg commands respectively:

 {{{
 ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 -f lavfi -i
 "sine=f=1000:d=10" -af "volume=0:enable=gt(mod(t\,1)\, 0.1)" -c:v libx264
 -crf 23 -pix_fmt yuv420p -t 10 test_no_shortest.mp4
 ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 -f lavfi -i
 "sine=f=1000:d=10" -af "volume=0:enable=gt(mod(t\,1)\, 0.1)" -c:v libx264
 -crf 23 -pix_fmt yuv420p -t 10 -shortest test_shortest.mp4
 ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 -f lavfi -i
 "sine=f=1000:d=10" -af "volume=0:enable=gt(mod(t\,1)\, 0.1)" -c:v libx264
 -crf 23 -pix_fmt yuv420p -t 10 -fflags +shortest test_mux_shortest.mp4
 }}}

 The following ffmpeg command can then be used to reproduce the problem:

 {{{
 ffmpeg -stream_loop -1 -i ffconcat.txt -c copy -f null -
 }}}

 where the contents of the ffconcat.txt are simply:

 {{{
 ffconcat version 1.0

 file test_no_shortest.mp4
 file test_no_shortest.mp4
 }}}

 Notice the `Application provided invalid, non monotonically increasing dts
 to muxer` errors.

 Now simply update the ffconcat.txt file and change each file line to
 `test_shortest.mp4` (which used the `-shortest` option) and run the ffmpeg
 command again. The errors are still present.

 Finally update ffconcat.txt file and change to `test_mux_shortest.mp4`
 (which used the `-fflags +shortest` option) and re-run the ffmpeg command.
 The errors are gone!

 Now I don't know ''why'' `-fflags +shortest` is fixing the issue in this
 case, but I have not figured out any other way to not have these errors
 without using this format flag on many of my input files.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11374>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker