Troubleshooting
Why Your Video Will Not Play, and How to Work Out Which Part Is Wrong
Sound but no picture, picture but no sound, or nothing at all. Each symptom points at a different cause, and none of them usually means the file is broken.
4 min read · Published 15 August 2026
A video that will not play is almost never a damaged file. Far more often the file is perfectly intact and the player simply cannot read one part of it. The useful thing is that each way it fails points at a different part, so the symptom tells you where to look.
First, the distinction that explains most of this
A video file is a container holding separate streams. MP4, MOV, MKV and WebM are containers. Inside sit a video stream compressed with one codec and an audio stream compressed with another, plus an index and any subtitles.
A player has to handle all of that: open the container, decode the video codec, decode the audio codec. Any one of the three can fail on its own, and that is why the failures look so different from each other.
| What you see | What is usually wrong |
|---|---|
| Sound plays, screen is black or green | The video codec is not supported |
| Picture plays, no sound at all | The audio codec is not supported |
| Player refuses to open the file at all | The container is not supported, or the index is damaged |
| Plays but stutters badly | The device is decoding in software because it lacks hardware support |
| Plays to a point, then stops | The file is genuinely incomplete, usually an interrupted transfer |
| Colours look washed out or oddly dark | A colour space or HDR mismatch, not a fault in the file |
Sound but no picture
This is the most common one, and it nearly always means H.265, also called HEVC. It is very efficient, it is what many phones now record in, and support for it is patchy: good on modern phones and televisions, unreliable in browsers and on older computers.
The giveaway is that everything else works. The container opened, the index was read, the audio decoded. Only the picture failed, which isolates the problem to one stream.
The fix is to re-encode the video stream to H.264, which plays essentially everywhere. It costs a generation of quality and some time, and it is the only reliable answer if the destination device cannot be changed.
Picture but no sound
The mirror image, and usually a codec the container was not expected to carry. Opus audio inside an MP4 is a frequent cause: Opus is excellent and belongs naturally in WebM, and putting it in an MP4 produces a file that many players open happily and then play in silence.
Before assuming a codec problem, rule out the obvious. Check that the file has an audio track at all, that the player is not muted, and that the correct output device is selected. A surprising share of silent videos are silent for one of those three reasons.
Will not open at all
Two possibilities, and they are easy to tell apart.
If other files of the same type open fine, this one is probably damaged, most likely an interrupted transfer or download. The index that tells a player where every frame sits usually lives at one end of the file, so a truncated download can leave the data intact and the map missing.
If no file of that type opens, the container itself is unsupported. MKV is the usual culprit on players that only expect MP4. This is the case where remuxing helps: the streams are moved into a different container without being decoded, which takes seconds and loses nothing at all. Re-encoding an hour of video to solve what remuxing fixes in thirty seconds is a common and expensive mistake.
Plays, but stutters
The device is decoding in software because it has no hardware support for that codec, and the processor cannot keep up. It is most visible with H.265 or AV1 on older machines, and with high resolutions and frame rates generally.
You will usually notice the fan and the battery before anything else. A file that stutters on one device and plays perfectly on a newer one is showing you exactly this.
A checklist that narrows it down
- Try the same file in a different player. If it works there, the file is fine and the first player is the problem.
- Try a different file of the same type in the original player. If that fails too, the container or codec is unsupported rather than this particular file being bad.
- Note precisely which part failed: picture, sound, or opening. That single observation isolates most causes.
- Check the file size against what it should be. A file much smaller than expected was truncated in transfer.
- Read what the file actually is, rather than guessing from the extension.
The video file information tool on this site reads a file's duration, dimensions and size in your browser without uploading it. If it opens there, the file is intact and readable, which rules out damage immediately. If it refuses, that is a codec the browser cannot decode.
One case where nothing will help
Protected content will refuse to play outside the app or service it belongs to, and that is deliberate rather than a fault. No amount of converting or remuxing changes it, and working around a protection measure is separately unlawful in many countries. If a file is protected, the answer is to play it where it is meant to be played.
Common questions
Why does my phone video play on the phone but not on my computer?
Most likely the phone recorded in H.265, which modern phones handle natively and older computers often do not. The file is fine; the computer cannot decode that codec. Re-encoding to H.264 fixes it for that machine.
Does renaming the file extension help?
No. Renaming changes nothing inside the file. It usually makes things worse, because the player trusts the new extension and then fails in a more confusing way.
What is the difference between remuxing and converting?
Remuxing moves the existing streams into a different container without decoding them: seconds of work, no quality loss. Converting decodes and re-compresses everything: much slower, and it always loses a little quality. Try remuxing first when the codec is supported and only the container is not.
The video plays but the colours look wrong. Why?
Usually a colour space or HDR mismatch rather than a fault. HDR footage shown on a display or player that does not handle it often looks washed out and flat. The file is unchanged; the interpretation is wrong.