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Need help?CAVS to M4R: Why a Raw CAVS File Cannot Become a Ringtone
A .cavs file is a raw Chinese AVS1 video bitstream, the video part of China's first-generation Audio Video Standard, GB/T 20090.2-2006. It is an elementary stream: coded pictures and nothing else, with no container to hold a parallel audio track. An iPhone ringtone is pure sound, so the honest answer for a true .cavs file is that there is nothing to make a ringtone from. This page extracts an audio track and re-encodes it as AAC in an .m4r file, the extension iPhone uses for custom ringtones; when the source has no audio, no setting can create it.
What you probably want is the soundtrack of the AVS video. That lives in the file the .cavs stream was taken from, and that file can become a ringtone.
Where the Audio Actually Is
In Chinese broadcast and set-top box workflows, AVS video and the audio are carried as separate streams and only joined in a container such as an MPEG transport stream, MP4 or MKV. Start from that container:
| What you have | Audio inside? | Page to use |
|---|---|---|
Raw .cavs elementary stream |
No | None; there is no sound to extract |
MPEG transport stream (.ts) from a broadcast or set-top recording |
Yes, usually MP2, AC-3 or AAC | TS to M4R |
| MP4 with AVS video and audio | Yes | MP4 to M4R |
| MKV with AVS video and audio | Yes | MKV to M4R |
| A separate AC-3 audio file from the same capture | Yes | AC3 to M4R |
To check a file, open it in VLC (Tools > Codec Information) or MediaInfo: a raw .cavs lists only a video stream.
How to Convert CAVS to M4R (If Your File Has Audio)
- Upload Your CAVS File: Drag the
.cavsonto the page or click "+ Add Files". If it turns out to be a raw stream, the container from the table above is the file to upload instead. - Trim to 30 Seconds or Less: Turn Trim on and set a Start time and a Duration, in seconds or
HH:MM:SS.sss. Apple says iPhone ringtones can be up to 30 seconds long, and the note under Duration says the same. - Set File Compression: Choose Constant Bitrate (8 to 384 kbps), Custom Bitrate, one of five Variable Bitrate bands (20k-32k up to 96k-112k) or Specific file size; Quality Preset is the hands-off mode. Audio Codec is AAC, the only codec for M4R.
- Convert and Download: Click Convert and save the
.m4r. Files are uploaded over HTTPS, processed on our servers and deleted automatically after a few hours. Free, no sign-up, no watermark.
A container that was saved with a .cavs extension by mistake may convert, but a true elementary stream has no audio stream to encode.
CAVS vs M4R
| Property | CAVS (source) | M4R (output) |
|---|---|---|
| What it is | Raw AVS1 Part 2 video elementary stream | AAC audio in an MPEG-4 container, .m4r extension |
| Standard | GB/T 20090.2-2006, from China's AVS Working Group | MPEG-4 and AAC; .m4r is Apple's ringtone extension |
| Audio | None | AAC-LC |
| Opens in | Specialist decoders and FFmpeg-based tools | iPhone as a ringtone; any AAC player |
| Comparable to | The H.264 generation of video coding | Not applicable |
| Length | Any | 30 seconds or less |
Settings Once You Have the Container
Broadcast audio from a transport stream is already lossy (MP2, AC-3 or AAC), so match it rather than exceed it: 128 kbps Stereo for music, 96 kbps Mono for speech. A 30-second ringtone is about 480 KB at 128 kbps (bitrate × seconds ÷ 8 = kilobytes). If the broadcast carried 5.1 AC-3, set Audio Channel to Stereo so the tone is an ordinary two-channel file.
How .cavs Files Usually Come About
People rarely receive a raw .cavs by accident. It usually appears when someone separates ("demuxes") the video from a broadcast recording or an MP4 for analysis, testing or re-encoding, or as a conformance test stream for checking AVS decoders. In every one of those cases the audio was either left behind in the original file or never existed. If you extracted the stream yourself, the original recording is still the place to start; if it came with other files, look for a matching .ts, .mp4, .mkv or a separate audio file with the same name.
Frequently Asked Questions
Why can't I get a ringtone from my .cavs file?
Because a raw .cavs holds only AVS video. There is no audio stream inside it, so there is nothing to make a ringtone from. Convert the transport stream, MP4 or MKV the video came from.
Is .cavs the same as an AviSynth .avs script?
No. AviSynth .avs files are text scripts for video processing, while .cavs is a coded AVS1 video stream.
How long can an iPhone ringtone be?
Up to 30 seconds, per Apple's support article on custom ringtones; GarageBand for iPhone also caps exported ringtones at 30 seconds. The 40-second figure in iTunes-era guides is not in Apple's current documentation.
Once I have an M4R, how do I put it on my iPhone?
Connect the iPhone to a Mac and drag the file onto it in the Finder sidebar (macOS Catalina or later), or use iTunes on Windows. It then appears in Settings > Sounds & Haptics > Ringtone and can be set per person via Contacts > Edit > Ringtone. Or save it to Files, import it into GarageBand on the iPhone and use Share > Ringtone.
Do Android phones need M4R?
No. Android ringtones are usually MP3 or OGG, so convert the container that holds the audio to MP3 instead.
Is my file stored?
Only briefly. It is uploaded over TLS, processed on our servers and deleted automatically after a few hours, and it is never shared or made public.