Manatee

Can you get the audio out of a video that will not play?

· 6 min read

Often, yes. Sound and picture are stored as separate tracks inside one file, and damage or an unsupported codec on the picture side frequently leaves the audio untouched. If QuickTime Player opens the file at all, File > Export As > Audio Only gets you the soundtrack in a minute; if it will not open, converting the video to a format QuickTime does read usually gets you there; and if the file’s structure is broken, it needs a repair before anything can read either track.

This is the recording of the talk where the picture fell apart halfway, the speeches at a wedding where the phone glitched, the grandparent telling a story while the camera pointed at the ceiling. The picture would be nice. The voice is the point.

Why the sound often outlives the picture

A video file interleaves two streams in chunks: a run of video frames, a run of audio, more video, and so on. They use different codecs and different decoders, and a player can fail on one while handling the other perfectly well.

Three things tilt the odds toward the audio surviving:

  • Size. A phone recording spends many times more data on the picture than on the sound, so a random damaged stretch is far more likely to land in picture data.
  • Simplicity. Phones and most cameras record AAC or uncompressed PCM audio, which every Mac decodes. The video side varies much more: HEVC, 10-bit HDR, VP9, AV1, older camera formats.
  • Fragility. Most video frames are stored as changes from earlier frames, so one damaged frame can smear across everything until the next full frame, which can be a second or more away. Damaged audio is usually a click or a short gap.

Find out what the file still has

Two quick looks, neither of which changes the file.

  1. Get Info. Select the file and press Command-I. Under More Info, a file with a readable index shows a Duration and usually its Codecs, for example HEVC and AAC. If those lines are missing entirely, the index is probably gone; skip ahead to the repair section.
  2. QuickTime Player. Double-click the file. If it opens, choose Window > Show Movie Inspector. The Format line lists the tracks; if it mentions AAC or another audio format, there is sound to export. Press play and listen past the point where the picture breaks. If the voice carries on, you are in good shape.

If the inspector lists no audio format at all, the file most likely has no sound track, and no tool can extract one. That is usually a microphone that was muted, not selected, or not allowed, rather than damage.

If QuickTime opens it: export audio only

  1. Optional: choose Edit > Trim to keep only the part you want, such as the twenty minutes of the talk itself. Drag the yellow handles at either end of the strip, then click Trim.
  2. Choose File > Export As > Audio Only.
  3. Name the file, choose where to save it, and click Save. You get an M4A file with the soundtrack.

If the export stops partway with an error, the damage reaches the audio as well, or the structure of the file is broken. Move on to the next sections.

If QuickTime will not open it: convert the video first

QuickTime Player only reads the formats macOS supports, and it gives up on damage that other decoders work around. A file it refuses can still have a perfectly readable soundtrack. The way through is to make a copy QuickTime can read, then export the sound from that.

  1. Open Manatee, choose Convert, drop the video in and pick MP4. It accepts most video files you are likely to meet, including MKV, AVI, WMV, MTS and old 3GP phone clips. The new MP4 is written next to the original, which is never modified, and nothing is uploaded anywhere.
  2. Open the new MP4 in QuickTime Player, check the sound plays, and choose File > Export As > Audio Only. You get an M4A.
  3. If you need a different format, drop the M4A into Manatee’s Convert and pick MP3 or WAV.

Manatee does not turn a video straight into an audio file; the audio targets are for audio you already have. The extra step costs a minute or two on a long recording.

Which audio format to end with:

  • M4A keeps the file compact and plays on every Apple device.
  • MP3 plays on practically anything, including old car stereos and forms that insist on it.
  • WAV is uncompressed and large, a sensible choice if the recording is going into an audio editor or to someone who will transcribe it.

The trade-offs between those, and the built-in QuickTime-plus-Music route to an MP3, are in How to convert MP4 to MP3.

Converting reads what can be decoded. A stretch of damaged audio still comes out as a click, a dropout or a moment of silence; a conversion does not restore it.

If the file is broken: repair first, then export

When a file has lost its index, which is common after a dead battery, a crashed recording app or a card pulled out early, neither QuickTime nor a converter can find either track. If a converter or upload page reported “moov atom not found”, this is your case; Moov atom not found explains what can and cannot come back.

  1. Open Manatee, choose Repair, and drop the video in. You can also right-click it in Finder and choose Services > Fix with Manatee.
  2. Read the outcome: Fixed, Partial (for example, the first eleven minutes of a longer recording) or Not fixable. The repaired file is a new copy beside the original, which is left as it was.
  3. Open the repaired copy in QuickTime Player and choose File > Export As > Audio Only. If it still will not open, convert it to MP4 first as in the section above.

A rebuilt file can come back with picture and sound of different lengths, because damage rarely falls in the same place for both. The sound you get is the sound the file held. If the picture comes back and the sound does not, the audio data could not be located, and there is nothing to export.

If your file is the opposite case, sound playing over a black picture, the audio is already fine and the post on a video that plays audio but shows a black screen explains what is wrong with the picture.

What cannot be recovered

  • Sound that was never recorded. A muted or unselected microphone, or a screen recording made without microphone access, produces a file with no audio track at all.
  • Anything after the cut. If the battery died at minute 40, minute 41 does not exist anywhere in the file.
  • A file of 0 bytes. There is no data in it to extract.
  • Damage inside the audio itself. Clicks and gaps stay. Manatee is not an audio editor: it does not clean up, denoise or boost a recording.
  • Deleted videos. Manatee works on files you already have. It does not recover deleted files from a card or a disk.

Before you give up, ask around. At a talk or a family event, somebody else often recorded too: the organizer’s camera, the venue’s sound desk, a cousin’s phone. Any of them may hold the part yours lost.

Questions

Will the extracted audio sound worse than it did in the video? WAV adds no further compression. M4A and MP3 are compressed formats, and on a voice recording at normal settings the difference is hard to hear. No format can improve on what the microphone captured, so there is no gain in choosing a bigger file than you need.

Should I keep the broken video once I have the sound? Yes. Neither QuickTime nor Manatee changes it, and it is the only source if you later want the picture, or want to extract the sound again in a different format.

Can I get just one person’s speech out of a long recording? Export the whole soundtrack first, then trim it. QuickTime Player can open an M4A and trim it with Edit > Trim, the same way it trims video.