My copy of QuickTime (10.5) on Mojave (10.14.6) is duplicating the duration of (some) tracks I open with it. It isn't modifying the files themselves; it's just the track window that displays twice the time it should. The entire second half is just silence.

enter image description here

Quitting QuickTime Player and reopening it doesn't help. Neither does restarting my computer.

QuickTime 7.6.6 (of which I have the Pro version) also does this.

It seems to happen only with m4a files, but not with all m4a files.

What's going on, and how can I fix it?

  • Use "quicklook" in Finder or iTunes or Elmedia to play it and see if it works fine there. Also, what is the file format ? I played some mp3 podcasts with and without the cover photo and they played fine, same 10.5 (935.3) version, 10.14.5
    – anki
    Commented Dec 29, 2019 at 7:48
  • I think the file in the screenshot is an m4a. I’ll check the other files and get back to you. When you say quicklook, do you mean playing it from Finder by clicking on the play button on the icon when in icon view / the Get Info window? If so, that only plays the correct duration, so it must be a QuickTime issue.
    – Rain
    Commented Dec 29, 2019 at 16:12
  • I've checked, and all the tracks it does that to are m4a files. However, it doesn't do it to all m4a files.
    – Rain
    Commented Dec 29, 2019 at 20:25
  • @Rain Hey, did you find the origin of this issue? I'm experiencing it right now. Thanks.
    – Alfonso
    Commented Sep 16, 2021 at 6:52
  • No, still haven’t found it. Sorry.
    – Rain
    Commented Sep 16, 2021 at 21:42

1 Answer 1


I experienced the exact same issue today and found that AVPlayerItem.seekableTimeRanges seems to return this incorrect duration.


What fixed the issue for me was to rename the audio from m4a/mp4to the contained audio format aac. E.g. myCoolAudioFile.m4a-> myCoolAudioFile.aac


What seems to be the root problem here is that Apple cant handle all container formats (I had a DASH container which caused this problem), to actually fix the root cause of this issue see here

  • This worked! Thanks! What a stupid bug on Apple's part...
    – Rain
    Commented Jul 17, 2022 at 18:52

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