Convert CAVS to 3G2 — Free Online Tool
Convert CAVS (Chinese Audio Video Standard) files to 3G2 format for CDMA mobile network compatibility. This tool re-encodes your CAVS video stream through H.264/libx264 and packages the result in a 3GPP2 container optimized for low-bitrate mobile delivery.
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 files use a proprietary Chinese national video codec that has very limited decoder support outside of mainland China. During this conversion, FFmpeg decodes the CAVS video stream entirely and re-encodes it as H.264 using libx264 — there is no stream copy shortcut available here because the source and destination codecs differ fundamentally. The audio, typically AAC in CAVS files, is similarly decoded and re-encoded as AAC for the 3G2 container to ensure clean compatibility. The output is wrapped in the 3G2 container (a close relative of MP4 developed for 3GPP2/CDMA networks), and the -movflags +faststart flag reorganizes the file's metadata index to the beginning of the file, enabling progressive playback before the full file has downloaded — a critical feature for mobile streaming.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In the browser-based tool, this runs via FFmpeg.wasm compiled to WebAssembly, so no files leave your device. For files over 1GB, copy this command to run it with a native FFmpeg installation on your desktop. |
-i input.cavs
|
Specifies the input file in CAVS format. FFmpeg will use its native 'cavs' decoder to decode the Chinese Audio Video Standard video stream contained in this file before re-encoding it. |
-c:v libx264
|
Re-encodes the decoded CAVS video stream using the libx264 H.264 encoder. This step is mandatory because the CAVS codec is incompatible with the 3G2 container and has no decoder on most mobile devices outside China. |
-c:a aac
|
Encodes the audio track as AAC, the default and most compatible audio codec for the 3G2 container. Even if the source CAVS file already contains AAC audio, a transcode ensures the stream conforms cleanly to the 3G2 format requirements. |
-crf 23
|
Sets the Constant Rate Factor for the H.264 encoder to 23, the standard default that balances visual quality and file size for mobile delivery. Lower values (e.g., 18) increase quality and file size; higher values (e.g., 28-35) reduce file size at the cost of more visible compression artifacts in the converted video. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, a standard quality level appropriate for speech and general audio in mobile-delivered 3G2 content. This is within the 3G2 format's supported audio bitrate range and balances audio clarity against the low-bandwidth constraints of CDMA networks. |
-movflags +faststart
|
Moves the 3G2 file's metadata index (moov atom) to the beginning of the output file after encoding completes. This is essential for mobile streaming over CDMA networks, as it allows playback to begin before the entire file has been received. |
output.3g2
|
Specifies the output filename with the .3g2 extension, which signals FFmpeg to use the 3GPP2 container format. This container wraps the H.264 video and AAC audio in a structure designed for CDMA mobile network transmission and playback. |
Common Use Cases
- Playing Chinese broadcast or government-issued video content on CDMA-based mobile devices (such as Verizon or Sprint legacy phones) that cannot decode the CAVS codec natively
- Archiving or redistributing Chinese digital television recordings in a container format understood by a wider range of mobile media players
- Preparing CAVS educational or training videos sourced from Chinese institutions for delivery over low-bandwidth CDMA networks where 3G2's compact structure is advantageous
- Converting CAVS content captured from Chinese set-top boxes into a format compatible with older mobile video platforms or MMS messaging systems that support 3G2
- Enabling video producers working with Chinese broadcast assets to distribute preview clips to field teams using CDMA mobile devices without requiring specialized CAVS decoders
Frequently Asked Questions
CAVS (Chinese Audio Video Standard) was developed as a domestic Chinese alternative to H.264 and has extremely limited decoder support outside of China-specific hardware and software. Very few international mobile devices, operating systems, or media players ship with a CAVS decoder. Converting to 3G2 replaces the CAVS video stream with H.264, which is a universally supported codec on mobile devices, so the resulting 3G2 file will play correctly on virtually any CDMA-era or modern mobile device.
Yes, this conversion is lossy at both stages. The CAVS video must be fully decoded and then re-encoded as H.264, which introduces generational quality loss — you cannot avoid this because the two video codecs are incompatible. The default CRF value of 23 used in this tool represents a standard quality level for H.264 that balances file size and visual fidelity well for mobile delivery. If your source CAVS file was already heavily compressed, lowering the CRF value (toward 18) will reduce additional quality loss at the cost of a larger output file.
3G2 is a direct descendant of the MPEG-4 Part 12 file format, making it structurally very similar to MP4, but it was specifically designed for 3GPP2 (CDMA) mobile networks and imposes stricter constraints on codec profiles and bitrates suited to low-bandwidth transmission. For this CAVS conversion, the key practical difference is that 3G2 includes the -movflags +faststart optimization and targets mobile-tuned H.264 profiles, making the output immediately streamable over a CDMA connection. If your target device or platform accepts MP4, that format may offer broader desktop compatibility, but 3G2 is the correct choice for CDMA mobile delivery.
By default, FFmpeg writes the MP4/3G2 'moov' atom (the metadata index describing the file's structure) at the end of the file, after all video and audio data. This means a player must download the entire file before it can begin playback. The +faststart flag causes FFmpeg to move the moov atom to the beginning of the file in a post-processing step, allowing mobile devices and streaming players to begin decoding the CAVS-sourced H.264 video as soon as the first bytes arrive over a CDMA connection.
The -crf flag controls H.264 quality on a scale from 0 (lossless) to 51 (worst quality). The default value of 23 is a good general-purpose starting point for mobile content. To reduce file size while accepting more quality loss — appropriate for very low-bandwidth CDMA delivery — increase CRF toward 28 or 35. To preserve more of the CAVS source quality, lower CRF toward 18. For example: ffmpeg -i input.cavs -c:v libx264 -c:a aac -crf 18 -b:a 128k -movflags +faststart output.3g2
Yes. On Linux or macOS, you can use a shell loop: for f in *.cavs; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.cavs}.3g2"; done. On Windows Command Prompt, use: for %f in (*.cavs) do ffmpeg -i "%f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "%~nf.3g2". The browser-based tool processes one file at a time, so the FFmpeg command is especially valuable for batch workflows involving large collections of CAVS content.
Technical Notes
CAVS decoding in FFmpeg relies on the native cavs decoder, which supports the video streams found in .cavs and AVS1-P2 compliant content but has limited support for edge-case profiles sometimes found in broadcast recordings. If your CAVS file was captured from a Chinese digital television source, it may contain MPEG audio rather than AAC; FFmpeg will handle the audio transcode transparently regardless. The 3G2 container does not support subtitles, chapters, or multiple audio tracks, so any of those elements present in a source file will be silently dropped during conversion — the tool outputs the primary video and audio streams only. H.264 encoded for 3G2 should ideally use Baseline or Main profile for maximum mobile device compatibility; libx264 defaults to Main profile at CRF 23, which is appropriate. Note that 3G2 audio bitrate options top out at 256k (versus 320k available in some other containers), which is more than sufficient for mobile delivery. File sizes will vary significantly depending on the complexity and resolution of the CAVS source, but the combination of H.264 at CRF 23 and AAC at 128k targets efficient compression well-suited for CDMA network constraints.