Convert CAVS to 3GPP — Free Online Tool
Convert CAVS (Chinese Audio Video Standard) video files to 3GPP format optimized for mobile devices. This tool re-encodes your CAVS video using H.264 (libx264) and AAC audio into a 3GP container with faststart optimization, making the output immediately streamable on 3G-compatible phones and low-bandwidth devices.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your CAVS file here
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Settings
Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
CAVS uses its own proprietary Chinese national standard video codec (AVS/AVS+), which has virtually no native support outside of Chinese broadcast and media ecosystems. During this conversion, FFmpeg fully decodes the CAVS video stream and re-encodes it from scratch into H.264 using libx264, targeting a CRF of 23 for a balanced quality-to-filesize ratio suited to mobile screens. The audio is transcoded to AAC at 64k — a conservative bitrate appropriate for 3GP's mobile-first design philosophy. The -movflags +faststart flag reorganizes the MP4/3GP metadata to the front of the file, enabling progressive playback on mobile networks before the full file downloads. This is a full transcode — both video and audio are decoded and re-encoded — so processing time will reflect the complexity of your source CAVS file.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. This command runs entirely in your browser via FFmpeg.wasm (WebAssembly) — the same command can be run locally on your desktop for files over 1GB. |
-i input.cavs
|
Specifies the CAVS source file as input. FFmpeg uses its built-in CAVS demuxer and decoder to read the Chinese Audio Video Standard video stream and its associated audio. |
-c:v libx264
|
Re-encodes the CAVS video stream using the libx264 H.264 encoder. Since CAVS has no native support in 3GP players, a full video transcode to H.264 is mandatory — stream copying is not possible here. |
-c:a aac
|
Transcodes the audio from the CAVS source to AAC, which is the standard audio codec for 3GP files and universally supported on 3G-compatible mobile devices. |
-crf 23
|
Sets the H.264 Constant Rate Factor to 23, providing a balanced quality level suitable for mobile screens. Lower values (e.g., 18) increase quality and file size; higher values (e.g., 28) reduce both — important when targeting bandwidth-limited 3G delivery. |
-b:a 64k
|
Sets the AAC audio bitrate to 64 kilobits per second, matching 3GP's mobile-optimized audio defaults. This keeps the output file compact for transmission over 3G networks while maintaining intelligible audio quality. |
-movflags +faststart
|
Moves the 3GP file's metadata index (moov atom) to the beginning of the file, enabling progressive streaming playback on mobile devices before the full file has downloaded — essential for 3G network delivery of converted CAVS content. |
output.3gp
|
Specifies the output filename with the .3gp extension, instructing FFmpeg to write a 3GPP-compliant container using the encoded H.264 video and AAC audio streams. |
Common Use Cases
- Distributing Chinese broadcast or educational CAVS video content to users on older 3G mobile devices that cannot decode AVS-format video natively
- Converting CAVS recordings from Chinese digital TV tuners or set-top boxes into a format playable on feature phones and entry-level smartphones
- Archiving or sharing Chinese sports broadcast clips (where CAVS is sometimes used) in a universally mobile-compatible container for field journalists or remote teams with limited bandwidth
- Preparing CAVS source video for MMS messaging or mobile video portals that require 3GP format for upload and streaming compatibility
- Converting CAVS training or instructional videos produced for Chinese domestic platforms into a format accessible to international mobile users on legacy devices
- Reducing the bitrate and container overhead of CAVS files for transmission over low-bandwidth or metered mobile connections where 3GP's compact encoding is advantageous
Frequently Asked Questions
Yes — this is a lossy-to-lossy transcode. The CAVS video is fully decoded and re-encoded into H.264 at CRF 23, which is a widely-accepted quality level but does introduce generation loss compared to the original. The audio is also re-encoded from its CAVS-embedded stream to AAC at 64k, which is noticeably compressed but appropriate for mobile playback on small speakers. If you need higher fidelity, you can lower the CRF value (e.g., 18) and raise the audio bitrate to 96k or 128k using the FFmpeg command directly.
3GP was designed specifically for 3G mobile networks and devices with limited storage and bandwidth. The format's audio quality defaults are intentionally conservative — 64k AAC is intelligible and functional on phone speakers and earbuds in mobile contexts. If your use case demands better audio fidelity (for example, if the CAVS source contains music or broadcast-quality dialogue), you can increase the bitrate to 96k or 128k by editing the -b:a flag in the FFmpeg command.
Yes, H.264-encoded 3GP files are broadly supported on modern Android devices via the native media player. iOS support for 3GP has historically been more limited, and newer iOS versions may require the file to be opened through a third-party app like VLC. If your target is modern smartphones exclusively, you may find MP4 with the same H.264/AAC codecs offers wider app compatibility, but for legacy 3G device support, 3GP remains the correct choice.
The +faststart flag instructs FFmpeg to move the moov atom (the metadata index that describes the file's structure) from the end of the file to the beginning. Without this, a media player must download the entire 3GP file before it can start playing. With faststart enabled, playback can begin as soon as the header is received — critical for streaming over slow 3G connections or when embedding video in mobile web pages. This is especially important since CAVS source files are often large broadcast recordings.
The video quality is controlled by the -crf flag, which accepts values from 18 (highest quality, largest file) to 28 (lower quality, smallest file) in this conversion's recommended range. For example, replacing -crf 23 with -crf 18 will produce a visibly sharper output at the cost of a larger 3GP file. Since CAVS is already a lossy format, avoid using very low CRF values — you will increase file size without recovering detail that was lost in the original CAVS encoding.
Yes. On Linux or macOS, you can use a shell loop: for f in *.cavs; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 64k -movflags +faststart "${f%.cavs}.3gp"; done. On Windows Command Prompt, use: for %f in (*.cavs) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 64k -movflags +faststart "%~nf.3gp". The browser-based tool processes one file at a time; the FFmpeg command is the recommended approach for batch jobs.
Technical Notes
CAVS (Chinese Audio Video Standard, also known as AVS1 or GB/T 20090) is a Chinese national codec standard with negligible decoder support outside of Chinese domestic hardware and software ecosystems. FFmpeg supports CAVS decoding but treats it as a specialized input format — no stream copying is possible when targeting 3GP, so a full video transcode is always required. The output 3GP container uses the MP4 box structure (it is essentially a constrained variant of MPEG-4 Part 12), which is why -movflags +faststart applies and functions identically to its use with MP4 files. H.264 Baseline or Main Profile is typically expected by legacy 3G devices; libx264 at CRF 23 will default to Main Profile, which has excellent 3G device compatibility. Neither CAVS nor 3GP supports transparency, embedded subtitles, chapter markers, or multiple audio tracks, so no metadata of those types will be present in either the source or output. If your CAVS file contains multiple audio tracks (uncommon but possible in broadcast recordings), only the first audio stream will be transcoded into the 3GP output. File sizes will typically be smaller than the CAVS source due to 3GP's low default audio bitrate and H.264's efficient compression at mobile-appropriate resolutions.