The 3GP file (.3gp, .3g2)

3GP is the video format that the 3rd Generation Partnership Project, the body that standardises GSM, UMTS and LTE mobile networks, defined for phones. It was designed for small screens, slow networks and limited processors: video messages (MMS), clips downloaded or streamed to a phone, and videos recorded with the phone's camera. Nokia, Sony Ericsson, Samsung and other phones of the 2000s saved their videos as .3gp, and Android phones offered it as a recording format for years.

Technically, a 3GP file is a member of the MP4 family: it uses the ISO base media file format, the same box structure as MP4 and MOV, with a 3GPP brand and a short list of codecs suited to phones. That's why many MP4 players open 3GP files, and why converting between them is often quick.

Each 3GPP release of the file format has its own brand in the ftyp box, and a file lists the brands it conforms to. The file format specification, 3GPP TS 26.244, gives these among others:

Mobile networks split into two families in the 3G era, each with its own standards body. 3GPP covered GSM and UMTS networks, used in most of the world; 3GPP2 covered CDMA2000 networks, used by some operators in North America and Asia. 3GPP2 defined its own variant of the file format, with the extension .3g2, the media type video/3gpp2, brands such as 3g2a, and support for the speech codecs of CDMA phones.

In practice both are opened by the same software, and VLC, mpv and FFmpeg treat them alike. A .3g2 that won't play usually fails for the same reason a .3gp does: its speech codec.

The most common 3GP complaint is a picture with no sound. The cause is almost always AMR audio. AMR is a speech codec designed for phone calls, and it's covered by patents licensed through a pool administered by VoiceAge. Phones and phone-oriented software include a decoder, but many desktop players, editors and web browsers don't, so they play the video and skip the audio track.

• Any system: VLC and mpv play 3GP and 3G2 files with every common codec, AMR included.
• Windows: the Media Player app plays many 3GP files; VLC handles the rest.
• macOS: QuickTime Player opens many 3GP files; VLC or IINA when it can't.
• Android: the built-in gallery and video players play 3GP. On an iPhone, use VLC.
• Edit: convert to MP4 first; most editors handle H.264 MP4 better than H.263 or AMR.

# any 3GP or 3G2 to an MP4 that plays everywhere
ffmpeg -i in.3gp -c:v libx264 -crf 20 -pix_fmt yuv420p -c:a aac -b:a 96k -movflags +faststart out.mp4

# H.264 video already? keep it, convert only the audio
ffmpeg -i in.3gp -c:v copy -c:a aac out.mp4

# what's inside
ffprobe in.3gp

HandBrake does the same with presets, if you'd rather use an app. Phone videos are small, so there's no reason to keep the low bit rate: the -crf 20 setting keeps what detail there is.

• Old personal content. 3GP files often come from old phone backups and MMS archives: private messages and videos of people who didn't expect them to be shared. Check before you put a batch online.
• Metadata. Phones could store the recording date, phone model and sometimes location. ffprobe lists the tags; ffmpeg -i in.3gp -map_metadata -1 -c copy out.3gp removes them.
• Decoder bugs. A 3GP file can't run code, but media parsers on phones have had serious flaws triggered by crafted files: the 2015 Stagefright bugs in Android could be set off by an MMS message. Keep phones and players updated.