My videos won't play in Quicktime - Why?

Reasons QuickTime Player May Not Open MP4 Files

QuickTime Player can't play MP4 files for many reasons. Before we dive into the solution, let's figure out what exactly causes the playback failure in your case.

1. The QuickTime Player stays in an old version.

If you are using old versions of QuickTime, MP4 videos compressed with recent codecs will not be supported. QuickTime Player 7 starts to support H.264 and newer versions in macOS High Sierra support HEVC/H.265. In QuickTime 10.0 or later versions, legacy media files will be converted automatically so that you can open MP4 files successfully.

And as the player was originally developed for macOS, there might be many bugs in Windows that result in MP4 playback errors in QuickTime.

2. The MP4 video was encoded with older or specialized codecs.

MP4 just refers to the format container or a video file with .mp4 in its name extension. How the video was encoded determines whether it can be opened by a player.

MP4 contains many sorts of video and audio codecs that may beyond the encoding and decoding capabilities of QuickTime. The video streams in MP4 files can be encoded in the MPEG-1, MPEG-2, MPEG-4, H.264/AVC, and H.265/HEVC standards. However, Apple claims that QuickTime does not support legacy or specifically-designed codecs and formats, and it only supports MP4 encoded with H.264, MPEG-4, and H.265/HEVC (since macOS 10.13).

3. The MP4 video is corrupted.

Improper file transfer, technical glitches, virus attacks, and many other factors may result in MP4 video file corruption. There's no easy way to know whether your MP4 is corrupted, but file corruption is always considered responsible for playback issues when we try to troubleshoot. QuickTime has no recovery features so it won't play MP4 if it's broken.

How to Fix QuickTime Player Can't Open MP4

No matter QuickTime can't play MP4 due to the player per se or the video file format, we found 3 feasible solutions corresponding to each cause. Read the instructions below to resolve the "QuickTime Player can't open files" error now.

Solution 1. Convert MP4 to QuickTime Format

If you don't want to try many solutions but end up getting it unresolved, converting MP4 to a format friendly to QuickTime works effectively all the time. All you need is software like Wondershare... or opt to play with VLC player instead.

Solution 2. Use Wondershare or a file converter like Nero.

Solution 3. Use VLC Media Player to Repair and Open MP4

Compared with QuickTime Player, VLC is more capable with a wide array of supported formats and codecs. What's more, it has in-built index repair tools to repair movie files indexes instantly. If QuickTime Player can't open MP4 due to file corruption, fix it with VLC.

Step 1. Change the extension of the .mp4 file into .avi because the repair feature is only workable for AVI videos.

Step 2. Open Finder and open VLC in it.

Step 3. Click VLC > Preferences > Input/Codecs. Find the Damaged or incompatible AVI files option, expand its drop-down menu, and choose Always fix. Save the settings.

The Bottom Line

MP4 playback errors in QuickTime Player can be solved by format conversion or transcoding in most cases. Instead of switching from one method to another, many Mac users prefer using a handy video converter to resolve this matter once and for all.