Manatee

How to convert 3GP phone videos to MP4 on a Mac

· 6 min read

A 3GP file is a close cousin of MP4, so the container is rarely the problem; the old codecs inside it are. Try opening the file in QuickTime Player first. If it plays, File > Export As will give you an MP4. If QuickTime says the file is not compatible, Manatee will convert it to a standard MP4 that plays anywhere, using decoders for the old phone codecs that macOS no longer includes.

What is inside a 3GP file

3GP (and its 3G2 variant for CDMA networks) was the video format of feature phones and early smartphones. It is defined as a restricted version of the MP4 container, which is why the two feel so similar: same structure, same box layout, similar headers. The difference is what the phones put inside.

Video was usually H.263 or MPEG-4 Part 2 (Simple Profile) at resolutions like 176x144 or 352x288, and later H.264 on better phones. Audio was usually AMR-NB, a narrowband speech codec that makes everything sound like a phone call, sometimes AMR-WB or AAC on later devices.

Modern macOS plays H.264 and AAC without complaint. H.263, MPEG-4 Part 2, and AMR were supported by the old 32-bit QuickTime framework that Apple removed in macOS 10.15 Catalina. On any Mac from the last several years, a 3GP with those codecs either fails to open or plays video with no sound (AMR being the missing piece), even though the container is essentially MP4.

So “converting 3GP to MP4” really means “re-encoding old codecs into codecs that today’s devices play.” That is why renaming the file does not work: the extension changes, the codecs do not.

Find out what you are dealing with

  1. Select the .3gp file in Finder and press Command-I (Get Info).
  2. Look under More Info for Codecs. Something like “H.264, AAC” means the file will probably play as is. “H.263” or “AMR” means it needs re-encoding.
  3. If Finder shows no codec information, open the file in QuickTime Player and choose Window > Show Movie Inspector. If QuickTime cannot open it at all, that is your answer.

If the file shows H.264 and AAC, you can rename it from .3gp to .mp4 in Finder and most players will accept it. For a proper remux that rewrites the container without touching the video, the ffmpeg stream-copy command further down does it with no quality change.

Convert with QuickTime Player (if it opens the file)

  1. Open the 3GP in QuickTime Player.
  2. Choose File > Export As and pick a resolution. Choose the one closest to the original; 480p is already larger than most 3GP videos, and picking 1080p simply scales a low-resolution picture up and wastes space.
  3. Name the file and click Save. QuickTime writes an MP4 (it may use the .mov extension on some versions; if so, the Export As menu also offers an MP4 option on recent macOS).

QuickTime re-encodes the video to H.264 and the audio to AAC. If the result has no sound, the original audio was AMR and QuickTime silently dropped it; use Manatee instead.

Convert with Manatee

Manatee accepts .3gp (along with .mp4, .mov, .avi, and the rest of its video inputs) and converts to MP4 using the ffmpeg engine bundled inside the app, which includes decoders for H.263, MPEG-4 Part 2, AMR-NB, and AMR-WB. It runs on macOS 12 Monterey or later, on Apple silicon and Intel, with nothing uploaded.

  1. Open Manatee and choose Convert.
  2. Drop the 3GP files into the window. A folder of a hundred old phone videos is fine; they queue up in the job list.
  3. Choose MP4 as the target.
  4. Click Convert. Each MP4 is written next to its original, and the 3GP files are never modified.

The output is a standard MP4 that plays in QuickTime Player, on iPhones, in browsers, and on TVs. Audio that was AMR is decoded and written as ordinary stereo-capable audio, so the sound comes back.

What Manatee will not do: it does not add detail that was never captured. A 176x144 video stays a 176x144 video, now in a modern container. It does not upscale, denoise, deinterlace, stabilize, trim, or join clips; it is a converter, not an editor. And if a 3GP was itself damaged (a common fate for files that sat on a memory card for fifteen years), Convert may fail, in which case Manatee’s Repair mode is the next step, with an honest Fixed, Partial, or Not fixable result.

If you have ffmpeg installed

Re-encode to a modern MP4:

ffmpeg -i clip.3gp -c:v libx264 -crf 20 -c:a aac -b:a 128k clip.mp4

If Get Info already shows H.264 and AAC, remux without re-encoding:

ffmpeg -i clip.3gp -c copy clip.mp4

ffmpeg is not part of macOS; the Manatee route exists so you do not have to install it.

Getting the most out of an old video

Expect the converted file to look exactly as rough as the original. These videos were shot on phone sensors of the era at bitrates measured in tens of kilobits. A modern 4K display will show every block. A few practical notes:

  • Do not pick a huge output resolution. Scaling a 320x240 clip to 1080p makes the file larger and blurrier, not better. Keep the source size.
  • Dates. The 3GP’s recording date is usually in the file’s metadata and is carried into the MP4. If the Photos app shows the wrong date after import, fix it with Image > Adjust Date and Time.
  • Rotation. Some phones recorded sideways and stored a rotation flag. Manatee and ffmpeg honor it; if a video comes out rotated, the flag was missing from the source and the video needs rotating in QuickTime (Edit > Rotate Left or Right, then export).
  • Odd lengths. Very old 3GPs sometimes show a wrong duration. If the MP4 stops early, see video file shows the wrong length.
  • Files that will not convert at all are usually truncated. How to check whether a video file is corrupted on a Mac walks through the diagnosis.

Questions

Can I just rename .3gp to .mp4?

Only if the file already uses H.264 and AAC, which is true for 3GPs from later smartphones. For anything using H.263 or AMR, the renamed file will still fail to play or will play silently.

Why does the converted video have no sound?

The converter could not decode AMR audio. QuickTime Player drops AMR. Manatee and ffmpeg decode it.

Will the MP4 be bigger than the 3GP?

Often, yes, by a modest amount. H.264 is far more efficient than H.263, but converters encode at a quality level that does not throw away what detail the original had, so a 2 MB clip may come out at 3 MB. It is still a fraction of the size of a modern phone clip.

QuickTime says the file is not compatible. Is it corrupted?

Usually not; it is the codec. See QuickTime says the file isn’t compatible: what to do for how to tell the two apart.