Damaged MP4 rejected by ffmpeg, mkvtoolnix can read it fine

[PumaD]

Got a multi GiB file which is unfortunately damaged and all players I tested refuse to play. I almost deleted it but then had the idea to run it though mkvtoolnix. It managed to salvage it almost completely with just minor visual artifacts during playback.

Would be great if ffmpeg could do the same.

How to reproduce:

$ ffmpeg -i slightly-damaged.mp4 out.mp4
ffmpeg version N-115112-g39ce8a9695 Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13.2.1 (GCC) 20240417
  configuration: 
  libavutil      59. 17.100 / 59. 17.100
  libavcodec     61.  5.103 / 61.  5.103
  libavformat    61.  3.103 / 61.  3.103
  libavdevice    61.  2.100 / 61.  2.100
  libavfilter    10.  2.101 / 10.  2.101
  libswscale      8.  2.100 /  8.  2.100
  libswresample   5.  2.100 /  5.  2.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x609423feb840] Invalid sample size -1251017134
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x609423feb840] error reading header
[in#0 @ 0x609423feb580] Error opening input: Invalid data found when processing input
Error opening input file slightly-damaged.mp4.
Error opening input files: Invalid data found when processing input

Tested with ffmpeg 6.1.1 as well as git master from yesterday.

[PumaD]

I've uploaded a sample under the name slightly-damaged-refuses-to-play.mp4 to ​https://streams.videolan.org/upload/ since it's too big to attach here.

[MasterQuestionable]

͏    MKVToolNix..?
͏    ​https://gitlab.com/mbunkus/mkvtoolnix#1-introduction

͏    Sure it's MP4?
͏    What's your ​`mkvmerge` command? (if indeed MP4 input)

͏    FFmpeg much relies the filename extension: when ͏"-f" not specified.

[MasterQuestionable]

͏    Indeed MP4:
͏    ​https://streams.videolan.org/ffmpeg/incoming/11005/slightly-damaged-refuses-to-play.mp4 (~ 6.35 MiB)

͏    Note: NSFW

[PumaD]

Replying to MasterQuestionable:

͏    MKVToolNix..?
͏    ​https://gitlab.com/mbunkus/mkvtoolnix#1-introduction

Yes, that one. Sorry, I shouldn't have assumed everyone to be familiar with it.

͏    Sure it's MP4?

Your implication being that MKVToolNix can only read MKV and not MP4? That's not the case. It can only create MKV but read a very wide variety of input formats.

͏    What's your ​`mkvmerge` command? (if indeed MP4 input)

I used the GUI, but that only constructs a command line. A simple mkvmerge --output out.mkv slightly-damaged-refuses-to-play.mp4 works.

͏    FFmpeg much relies the filename extension: when ͏"-f" not specified.

Good to know, I wasn't aware of that. However, you already confirmed in your other comment that it's indeed MP4.

[MasterQuestionable]

͏    Thanks for feedback.
͏    I much figured out the cause. (though unable to provide fix now)