Fixing "file is not supported" and "unsupported video format" errors

By the FixMP4 engineering team · Updated October 9, 2026 · Tested on real H.264, HEVC and AAC recordings

"File is not supported", "unsupported video format", "The file isn't compatible with QuickTime Player" and similar messages mean the app could not read the file. Usually the file is healthy and the app lacks a codec or does not support the container. Sometimes the file really is damaged, typically an MP4 or MOV whose index is missing after a recording was cut off. Test the file in VLC: if VLC plays it, fix the app (codec, update, convert); if VLC fails too and the file is large, rebuild the index. You can check the second case for free with the FixMP4 repair tool.

Where you see this message

Step 1: the VLC test

Open the file in VLC on a computer. VLC includes decoders for almost every format.

• It plays: the file is fine. Go to step 2.
• It does not play, or shows 0:00: the file is damaged or incomplete. Go to step 3.

Step 2: the file is fine, make the app happy

• Check the codec: in VLC, Tools, Codec Information shows the codec. HEVC, AV1, VP9 and ProRes are frequent culprits on older devices.
• Install codec support: on Windows, the HEVC and AV1 extensions; on older Macs, update macOS.
• Convert a copy: HandBrake's "Fast 1080p30" preset produces H.264 + AAC in MP4, which almost every device accepts.
• Change the container: MKV to MP4 remuxing (without re-encoding) helps QuickTime and many TVs.
• Update the app or firmware: smart TVs and car systems gain codecs with updates.
• For future recordings, choose H.264 (Most Compatible on iPhone) if you need broad compatibility.

Step 3: the file is damaged

If no player opens the file, check its size. A large file means data is present; a 0-byte file means nothing was written (see MP4 is 0 bytes).

For a large MP4, MOV or M4A that will not open anywhere, the most common damage is a missing index (moov atom) caused by a recording or transfer that stopped abruptly. To fix it:

1. Record a short reference on the same device with the same settings (not needed for AAC audio like Voice Memos).
2. Open the repair tool and add both files.
3. Watch the free preview and export with a subscription.

After the rebuild the file plays in VLC; whether a particular TV or app accepts it then depends on codec support, as in step 2.

Special cases

Android: hidden .pending files

On Android 10 and later, an interrupted recording may remain as a hidden file whose name starts with ".pending-" in DCIM/Camera. The Gallery calls it unsupported or does not show it. Copy it to a computer and repair it; see fix Android video.

Files received in messaging apps

Apps sometimes deliver partial downloads. Download again before repairing.

Screen recordings and game captures

If a recorder crashed, the MP4 has no index; see recover an OBS recording.

CCTV exports

Many security recorders export proprietary streams with an .mp4 extension. These are not corrupted, just not standard; see fix CCTV / DVR video.

Why renaming does not help

Renaming .mov to .mp4 (or the reverse) can help with a picky app, because the two containers are closely related. It does not fix damage: a file without an index stays unreadable whatever its name. Renaming to .avi or .mkv makes things worse, because the content is not AVI or MKV.

How the repair works

FixMP4 reads the damaged file locally in your browser, finds each H.264 or HEVC video frame and each AAC audio frame in the raw data, takes codec parameters from your reference, and writes a new standard index. Nothing is re-encoded and nothing is uploaded.

Checking the codec quickly

To see exactly what a file contains, use MediaInfo (free, Windows and Mac) or VLC's codec information. Look for three things: the container (MPEG-4, QuickTime, Matroska), the video codec (AVC/H.264, HEVC/H.265, AV1, ProRes) and the audio codec (AAC, AC-3, Opus, PCM). Compare them with what your app or device supports, which is usually listed in its manual or support pages. If MediaInfo cannot identify the container at all and the file is large, the file is probably damaged.

Common mistakes

• Converting a file that is actually damaged; converters need a readable index and fail or produce an empty file.
• Repairing a file that is healthy; if VLC plays it, the issue is codec support.
• Deleting the original after a failed attempt.

Related error guides

• Error 0xc00d36c4
• "Invalid data found when processing input"
• Repair an MP4 file
• All error guides

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