Manatee

What an OGM video file is, and how to convert it on a Mac

· 6 min read

An OGM file is a video from the early 2000s: an unofficial use of the Ogg container to hold the DivX and Xvid video of the day, Vorbis audio, and often several audio languages and text subtitles. No app that comes with macOS plays one. To watch it, or to keep it with the rest of your video, convert it to MP4 with the video re-encoded to H.264, and decide first which audio and subtitle tracks you need.

Where OGM files came from

Ogg is an open container designed mainly for audio. Its official video format is Theora, which uses the .ogv extension, and an OGV is a different thing; how to convert an OGV video to MP4 covers those.

OGM was a workaround by people who wanted Ogg’s features for the video codecs they already used. It could carry several audio tracks and several subtitle tracks in one file, which AVI could not do cleanly, so for a few years it was a common choice for shared DVD rips and fan-subtitled series. Matroska (MKV) took over that role and OGM faded, which is why these files mostly turn up on old hard drives and backup discs.

Why a Mac will not play it

macOS plays video in MP4 and MOV containers holding codecs such as H.264, HEVC or ProRes, with audio such as AAC. An OGM fails on every count. QuickTime does not know the container, the DivX or Xvid video inside is an older MPEG-4 codec Apple players do not reliably decode, and Vorbis audio is not something QuickTime plays. Finder shows a plain icon with no preview, and double-clicking gets you a message that the file is not compatible.

That combination is also why renaming will not help. Change .ogm to .mp4 and the contents are exactly as foreign as before.

Check what is inside before converting

An OGM can hold more than one audio track and more than one set of subtitles, and a conversion that keeps only the first of each may keep the wrong language. If you have ffmpeg installed, ffprobe lists every stream:

ffprobe -hide_banner movie.ogm

Each line that begins Stream #0: is one track: video first, then audio (with a language code if the file has one), then subtitles. Note the ones you want to keep. Without ffprobe, open the file in any media player that handles OGM and look through its audio and subtitle menus.

Converting with Manatee

Manatee reads OGM files directly and converts them to MP4 or MOV. It bundles its own copy of ffmpeg, so there is nothing else to install, and it runs entirely on the Mac with nothing uploaded.

  1. Open Manatee and choose Convert.
  2. Drop the OGM files into the window, or onto the menu bar icon.
  3. Pick MP4 as the target. Choose MOV only if the file is going into an Apple app that prefers it.
  4. The converted file is written beside the original, which is never modified.

Manatee re-encodes the old video to H.264, which every current Apple device plays. It is free for 24 hours with every feature, then $9 once.

One thing to check yourself. If the OGM holds several audio or subtitle tracks, play the converted file and confirm the language and subtitles are the ones you want before you delete anything. For full control over which tracks are kept, the ffmpeg route below lets you name them.

Converting with ffmpeg in Terminal

If you already use ffmpeg, one command converts the video to H.264 and the audio to AAC, and the -map options choose the tracks:

ffmpeg -i movie.ogm -map 0:v:0 -map 0:a:1 -c:v libx264 -crf 20 -preset slow -c:a aac -b:a 160k movie.mp4

Here 0:a:1 means the second audio track; use 0:a:0 for the first. A -crf value from 18 to 22 keeps an old standard-definition picture looking as it did, and lower numbers mean larger files.

Text subtitles inside an OGM can usually be saved on their own as an SRT file:

ffmpeg -i movie.ogm -map 0:s:0 movie.srt

Give the SRT the same name as the MP4 and keep the two together, and players that load separate subtitle files will pick it up. If a subtitle file comes out with odd characters, subtitles that show strange characters covers the fix.

What to expect from the converted file

  • Picture quality. Most OGM files are standard definition, and re-encoding cannot add detail that was never there. A careful H.264 encode keeps what the source holds; it will not look like modern HD.
  • Size. H.264 compresses more efficiently than the codecs OGM files usually carry, so at similar quality the MP4 often comes out about the same size or smaller. Pushing the quality setting down to save space is where an old picture starts to smear.
  • Sync. If the sound drifts away from the picture in the result, audio out of sync after a conversion explains the usual cause and the fix.
  • The original. Keep the OGM until you have watched the MP4 through. It may hold audio or subtitle tracks the MP4 does not.

Questions

Is an OGM the same as an OGG? They share the Ogg container. An .ogg file is normally audio only. An .ogm is video built on the same structure in a way the format’s own maintainers never adopted, which is why support has always been patchy.

Can I convert an OGM to MKV instead? Yes. With ffmpeg it can usually be done without re-encoding, keeping every track. But a Mac does not play MKV either, so for watching on Apple devices MP4 is the better target. MKV files on a Mac covers that route.

Why does Finder show no preview for the file? Quick Look has no way to read OGM, so it shows a plain icon. That says nothing about whether the file is damaged; a working OGM looks exactly the same.