[FFmpeg-user] Remuxing TS to MP4 causes black frame in Apple playback scenarios

[Sid Sethupathi]

Hello,

I have a process that remuxes short HLS playlists into an mp4 format. The
output mp4 in this process has an all black first frame when played back in
either Safari or Quicktime Player. Everywhere else, the first frame does
not have this black frame.

The process is an internal tool that uses libav directly so it's hard to
share the code, but I think I can reproduce via an ffmpeg command line
invocation against a single TS segment, so I'm hoping to be able to solve
the problem by understanding how to change the ffmpeg command.

All the sample files can be found in this public Google Drive:
https://drive.google.com/drive/folders/1L8T5T4l_GUzxRnhjH-ojnT6-44FQLQq1?usp=drive_link
.

bbb_2.ts is the second segment of Big Buck Bunny (sourced from this test
stream:
https://test-streams.mux.dev/x36xhzz/url_0/193039199_mp4_h264_aac_hd_7.m3u8).
If you open this ts file in Quicktime player or Safari, the first frame is
NOT black.

bbb_2_remuxed.mp4 has been remuxed using the following command: "ffmpeg -i
bbb_2.ts -c copy -f mp4 bbb_2_remuxed.mp4". If you open it up in Quicktime
Player or Safari, the first frame IS black. I think I traced it down to an
extra entry in the "elst" atom. If you probe this remuxed mp4 with trace
level debugging on ("ffprobe -v trace bbb_2_remuxed.mp4") there's a short
duration entry in the edit list of the video track.

[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fd357104bc0] type:'elst' parent:'edts' sz: 40
8 40
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fd357104bc0] track[0].edit_count = 2
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fd357104bc0] duration=15 time=-1 rate=1.000000
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fd357104bc0] duration=10000 time=2999
rate=1.000000

According to the Quicktime file format docs, the parent of the "elst" atom
is "edts" and it is optional, so I removed that atom using mp4edit in the
Bento4 tool kit. This produced "bbb_2_remuxed_no_edts.mp4". If you open
this file in Quicktime or Safari, the first frame is NOT black.

bbb_2_transcoded.mp4 is a transcoded version using "ffmpeg -i bbb_2.ts
-video_track_timescale 90K -movflags +faststart bbb_2_transcoded.mp4". If
you open this file in Quicktime or Safari, the first frame is NOT black. If
you inspect the atoms in this file, the video "elst" atom is still there,
but it only has a single entry in the list.

[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fe3ecf06040] type:'elst' parent:'edts' sz: 28
8 28
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fe3ecf06040] track[0].edit_count = 1
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fe3ecf06040] duration=10017 time=3000
rate=1.000000

So, ultimately I think the extra entry in the elst edit table is the cause
of the issue. My question is whether it is possible to not have that happen
via the ffmpeg/libav invocation, or whether this is a problem with the
source material?

Thanks,
Sid