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Common fix · Video

The video will not play

By Updated How we write these

2 min read

What you’ll end up with

An MP4 that plays on whatever you are trying to play it on.

Nearly every "video will not play" problem is one of two things: the container is one the player does not accept, or the codec inside it is one the device cannot decode. The symptoms tell you which.

Converting to MP4 with H.264 solves both, and when the streams are already compatible it is a repackage that takes seconds and costs no quality at all.

What to do

  1. Read the symptom

    Player refuses to open it at all — the container is unsupported, typically MKV on an Apple device. Sound plays, picture is black — the audio codec is fine and the video codec is not, usually HEVC. Plays but stutters badly — it is decoding in software, often AV1 on older hardware.

  2. Convert it to MP4

    MP4 with H.264 is the most widely playable combination there is. The converter copies the streams across untouched when the container allows it, and only re-encodes when it has to — and it tells you which happened.

    Convert to MP4

  3. If it still will not play, force the re-encode

    A repackage keeps whatever codec was inside. If the codec was the problem, choose H.264 explicitly so the picture is genuinely re-encoded into something the device can handle.

Worth knowing

  • A file that plays on your computer but not on a TV or phone is a codec problem, not a corrupt file. Hardware decoders are much pickier than desktop players.
  • A genuinely damaged file — interrupted recording, failed card — is a different problem, and converting it will not help.

Questions

Why does my MP4 play sound but show a black screen?

The video codec inside is not supported, most often HEVC on a device without an HEVC decoder. Re-encoding the video to H.264 fixes it.

Is converting MKV to MP4 lossless?

Usually, yes. If the streams inside are MP4-compatible they are copied rather than re-encoded. Container vs codec explains why.

What format plays on everything?

MP4 containing H.264 video and AAC audio. Nothing else comes close for compatibility.

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