Please be forgiving to a video file format newbie, who has travelled far and wide all over the Web in search of a relatively simple question and hoped to get an answer (even a fairly complicated one would be fine!):

TL;DR: I have a broken MP4 which lacks a MOOV atom (neither at the beginning nor at the end). So, how do I create a new MOOV atom in order to fix the file?

And now for the expanded question (if you bother to read it), which shows the homework I've done so far...

What solutions I've found so far...

A quick search just here on video.stackexchange.com will get you a few dozens of similar questions and variations on the theme; do that search on Google, and you'll get a few hundreds more; even Quora has a few answers... To summarise most of them, here is what they usually say:

  1. "MP4 files can have a MOOV atom at the end (that's the usual way) but also at the beginning; here's a selection of N solutions to move the atom from one place to the other" (no, they aren't useful if you have no MOOV atom whatsoever)
  2. "You can use ffmpeg (or a gazillion similar utilities — most of which will use ffmpeg's library anyway — or even VLC [some versions seem to have a way to automatically fix broken videos — not my case, though]) to somehow magically extract part of your broken file, split it into bits, or even split it into individual frames, then reencode, and eventually you'll get a few sequences of frames out of the corrupted video, or even, with luck, a bit of continuous video which will play (sometimes only under VLC, sometimes only under mplayer, sometimes requiring [insert favourite video player here])" (all these suggestions are very nice, but all assume that at least there is a MOOV atom somewhere — or else all will fail)
  3. "Some tools (or commercial applications) can deal with corrupt data on faulty disks/pen drives/memory cards, by reading sectors directly from the underlying media and bypassing the FAT or whatever filesystem layer is used by the operating system, thus at least being able to recover part of your video, even if it's (possibly) out of order, incomplete, etc." (this may all be true, but does not help in my case, where the file is pristine and there is no problem whatsoever with the hardware where it's currently stored — the file is just missing a MOOV atom, so none of these tools will help)
  4. "A few tools, such as untrunc, may be able to repair a broken file, especially if the MOOV atom is missing at the end of the file because the video camera abruptly had its power cut (or some similar situation). There are also several commercial software solutions available which do the same (and are easier to use) or even web-based ones. Commercial applications usually have a demo/trial mode where you can at least recover some data to give you an idea if your particular file is repairable or not. Usually, such software requires a video made by the same video camera under the same circumstances, to be able to push the missing data from that video to the corrupt file." (so far, I've not managed to find the 'magic tool' which does exactly what is claimed... all I've tested will fail with a missing MOOV atom... no matter if the 'test video' has it, which could easily be copied — assuming that this will 'fix' anything, of course).

Why none of the above actually helped me out

Things may be explained a bit differently in one case or another, but after going through dozens of descriptions of 'solutions' out there, I'd say that most will fall in one of those four cases. The fourth case, of course, is the only one that may help in my case, but, so far, I've tried pretty much everything which can run on a Mac — aye, including a few commercial apps — and none will deal with the issue.

I've also found out that many of these tools — especially those that are commercial! — are little more than a GUI to ffmpeg/libav. Some even use hopelessly outdated versions of these; in some cases, they're compiled with them statically; in other cases, ffmpeg and its friends are packed with the application, which just calls it with whatever special parameters the developers have figured out that might help (or even work!) in most cases.

While I'm pretty sure that some of the tools I tried out may have non-ffmpeg/libav code, they haven't worked, either. What I seem to be able to conclude is that anything depending on ffmpeg/libav code will not work without a valid MOOV atom. Therefore, the trick — if there's one! — is to somehow 'extract' a MOOV atom from either a different file and/or re-create the MOOV atom from the existing data. While the former seems to be the most popular approach (and, as said, I've tested a dozen or so apps using that approach), none worked in my case; as to the latter approach, if it exists at all, it's not explicitly named in any of the tools I've tested out, so I cannot say if that's possible at all (i.e. it may be a very obscure and undocumented feature of ffmpeg but, so far, I have not come across an answer which mentions such feature; of course, commercial tools, for obvious reasons, may simply not document what exactly their tool is doing 'under the hood').

Whew. Wordy, I know! Let me just give you some assurance that, although I hardly understand what I'm talking about — namely, the complex structure of an MP4/MOV file — I have certainly done my best to figure out what is wrong with my file, and why all attempts I've tried out so far have utterly failed. My apologies in advance if I'm assuming wrong things about the MP4 format and/or just saying rubbish which makes no sense (such as 'reconstructing a MOOV atom out of existing frames on a movie' — perhaps such a thing is impossible to do, for reasons I don't understand).

What I know about my file...

  1. It certainly has data in it (i.e. not just garbage). Several of those utilities correctly figure out that it's a QuickTime stream; some can even identify a few atoms.

Here is an example from mp4dump:

[ftyp] size=8+12
  major_brand = qt  
  minor_version = 0
  compatible_brand = qt  
[wide] size=8+0

And this is the output from mp4info:

  major brand:      qt  
  minor version:    0
  compatible brand: qt  
  fast start:       yes

No movie found in the file

(weird that it knows about 'fast start', though...)

Here is the output of my own hacked utility (see below):

        Major brand: qt  
        Minor brand: 0
        Compatible brands: [qt  ]

        Size: 8
        Start: 20

        Size: 2305577342
        Start: 28

But none can find a single MOOV atom. Photoshop can import 'noise' from some frames — they look like frames, though, just so noisy that they become 'random pixels', that is, it's pretty much impossible to figure out what exactly that frame is supposed to be...

  1. I have 'similar' files, generated by the same video camera (the iPhone 8's 'selfie' camera in landscape format), so I can easily extract an existing MOOV atom (or any other) and 'glue' it elsewhere on an existing file, a procedure many of the mentioned tools consider a possible solution to a 'missing' MOOV atom — but none are actually able to do that with my video...

What I can theoretically do to fix things

(or: An attempt to start to answer my own question...)

I'm just a humble amateur programmer, which means that fully developing a new tool in order just to fix my own video is very likely out of the question (and furthermore I have no time for that). The best I can promise to do if nobody has an answer is to figure out how MP4 encoders actually generate a MOOV atom from the existing data and see if I can adapt an existing tool to 'regenerate' the MOOV atom from scratch (note: I did hack it a bit to show the contents of all atoms it can find inside the file when the MOOV atom is missing, the output of which I've given before)... alas, I think that this might be impossible if one does not know some basic things about the video file itself (after all, these 'basic things' are stored on the MOOV atom!), but I'm happy to be proven wrong on that — especially because I can 'guesstimate' many of those 'basic things' by simply reading the MOOV atom from a video file generated under similar circumstances...

Here is such an example (tracks 3 and 4 are not really fundamental):

found avc1
  file Size:    16072874
  brands:   qt  , [qt  ]

  duration: 6859 ms / 600 (00:00:11:431)
  fragments:    false
  timescale:    600

Found 4 Tracks

Track 1:
  id:       1
  type:     Video
  duration: 6859 ms
  language: und
  width:    1920
  height:   1080
    sample count:   184
    timescale:      600
    duration:       6859 (media timescale units)
    duration:       11431 (ms)
  display width:         1920
  display height:        1080
  frame rate (computed): 16.10

Track 2:
  id:       2
  type:     Sound
  duration: 6859 ms
  language: und
  width:    0
  height:   0
    sample count:   495
    timescale:      44100
    duration:       506880 (media timescale units)
    duration:       11493 (ms)

Theoretically, with a bit more hacking, I can also extract the precise position where each track begins and ends (assuming that's how the MP4 format works!) and whatever information may be needed to 'reconstruct' the MOOV atom...

What help I actually need

I do have access to the PDFs with the ISO/IEC 14496-12 standard which defines the MP4 file format but I haven't read them yet. In essence, what I need to understand is how MOOV atoms are created/generated from existing video data. I'm fine with downloading and installing any tool which I haven't mentioned previously (so long as they work either under macOS or any non-GUI Linux — I might be able to temporarily get access to a Windows 10 machine if I'm assured that there is a solution that will work under Windows). I'm also willing to change or adapt existing open-source tools, so long as I can get some pointers on how to actually 'generate' the MOOV atom from existing video data (preferably written in Go or PHP, but I'm ok with C, C++, C# or Python [in decreasing order of preference], or, well, Perl or JavaScript... I'm just not willing to install Java :-P and I'd really need a lot to get persuaded to use Ruby, Rust, or whatever language is currently fashionable...).

If you read until the end, my heartfelt thanks in advance :-)

  • I'm scared to ask, but curious, how did you end up in this situation, what is the video content you are recovering?
    – Ryan Leach
    Feb 23, 2020 at 15:15
  • Care to share the corrupt file? Feb 23, 2020 at 20:21
  • 1
    cough thanks for your questions/suggestions but let's just say that this particular video might not be safe for the workplace... May 2, 2020 at 20:37
  • 2
    @RyanTheLeach, as far as I could figure it out, what seemed to have happened was that the video capturing app on my iPhone unexpectedly crashed, just seconds before the end of the movie... so it had already captured all the data, but still hadn't finished writing out the index. I have no idea if that makes sense or not to you guys, but it seems that this was the case. In other words: if the index had somehow 'survived' the crash, I would probably lose some video (and sound sync might be gone, too), but at least I would get something. But without a MOOV atom... no luck! May 2, 2020 at 20:37

3 Answers 3


duplicate of How to recover a broken mp4 file: moov atom not found at unix.stackexchange.com - especially since you're looking for a linux/macos solution

limitation: the untrunc tool needs a working similar video file


As you said you have similar files, you may try the following:

1) any good mp4 file with the same resolution and bitrate to generate the header files:
recover_mp4.exe good.mp4 --analyze

2) recover streams from the corrupted file, for example:
recover_mp4.exe bad.mp4 recovered.h264 recovered.aac

3) join audio and video with ffmpeg:
ffmpeg.exe -r 30 -i recovered.h264 -i recovered.aac -bsf:a aac_adtstoasc -c:v copy -c:a copy recovered.mp4

recover_mp4 : https://codecpack.co/download/recover-mp4.html ffmpeg: https://www.ffmpeg.org/

I've just covered a mp4 with the above method - although sound is still corrupted, video is all good.

  • 2
    Sorry for just answering today… I did, in fact, come across that tool; I just had two problems with it — there is only a Windows version for it (I have a Mac, an iPad, an iPhone, and easy access to all sorts of Linux variants, but I do not have Windows...); and allegedly the programmer behind that tool, while still offering the old version for free, has moved on to create a video recovery service. The preview mode did not fix my issue, and I wasn't keen in paying for the commercial solution, which may not have worked either... May 2, 2020 at 20:48
  • 2
    Dear user000001 Your comment saved me - I repaired my broken mp4 file. Thanks!
    – MateuszC
    Oct 23, 2020 at 21:59

The mdat box in a MP4 contains the media payload but it is freeform. It is as good as gibberish on its own. The moov box identifies how many tracks there are, which codecs and their parameters those tracks contain, which portions of the data in the mdat correspond to which tracks, what their timestamps are..etc.

What MP4 repair utilities do, is use the track and codec descriptions from the moov box of the reference file and transpose them to the repair candidate. Then they use heuristics to identify each track's data in the candidate. This relies on the codec of each track sporting some consistent & known signature to locate the start of each packet. The timestamps are however unrecoverable. So, if there's no reference moov or a way to create a similar one, the file is essentially unrecoverable.

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