CAVS to M4A Converter

Convert CAVS to M4A: Read This First

A bare .cavs file is a raw Chinese AVS (AVS1) video bitstream — by design it carries picture only, with no audio track inside it. So if your goal is to pull a soundtrack out of a .cavs and save it as an M4A, there is usually nothing to pull: the resulting file would be silent. This page is honest about why, shows how the converter behaves, and points you to the file that actually holds your audio.

Why a Raw CAVS File Has No Sound

CAVS is the video half of China's first-generation Audio Video Standard. It is standardized as GB/T 20090.2-2006 — formally "Information Technology, Advanced Audio Video Coding, Part 2: Video" — adopted as a national standard in February 2006 by the AVS Working Group, which was founded in June 2002. The part numbered .2 is the video specification, and the .cavs extension names exactly that AVS1-P2 video bitstream. In FFmpeg it is handled by the cavsvideo raw video demuxer, which registers a single video stream and nothing else. A file saved with a plain .cavs extension is an elementary stream: a sequence of coded AVS video frames, with no container around them to hold a parallel audio track, so there is no sound to decode.

In Chinese broadcast and set-top-box workflows the picture is encoded as the AVS stream and the audio is carried separately, only joined ("muxed") later into a combined container such as an MP4, MKV, or transport stream. So a true .cavs on its own is mute. If you ran this conversion and got a silent M4A, that is not a bug in the converter — it is the raw AVS stream doing exactly what the format specifies.

Note: .cavs here means a raw AVS1 video elementary stream. Do not confuse it with .avs AviSynth script files, which are a different thing entirely. This page is about the video bitstream.

How to Convert CAVS to M4A

1. Upload Your CAVS File: Drag and drop your .cavs onto the page, or click "+ Add Files" to choose it from your computer. You can queue several files to process with the same settings.
2. Pick a Quality Preset: Open "Show All Options" and choose a Quality Preset for the AAC audio inside the M4A — start with the highest preset, then step down if you need a smaller file. M4A stores AAC, a lossy codec, so a higher preset spends more bits to stay closer to the source.
3. Set Bitrate, Channel, or Trim (Optional): Switch to Custom Bitrate, Constant Bitrate, or Variable Bitrate to pin an exact rate; Audio Channel and Audio Sample Rate default to Original, which copies the decoded audio untouched; and Trim grabs just a portion of the timeline.
4. Convert and Download: Click "Convert" and download your M4A. No sign-up, no watermark.

Walk-through: Will Your CAVS File Actually Have Sound?

Whether you get audio depends entirely on what you actually uploaded, because the AVS1 video specification defines only picture — any audio was carried alongside it as its own stream. The common cases:

• A true raw .cavs elementary stream: This is video only. An M4A made from it will be empty or silent — there is nothing inside to extract. Nothing in the settings can create a soundtrack that was never in the file.
• A container that was misnamed .cavs: Occasionally a muxed file (an MP4, MKV, or transport stream from a Chinese set-top box or karaoke export) gets saved with a .cavs extension. If your file is secretly a container with a real audio track, the converter will decode that track to AAC and wrap it in the M4A normally. But that is the exception, not the rule, and the AVS decoder may simply reject a file that is not a raw stream.
• You actually want the soundtrack of an AVS video: then you are starting from the wrong file. Upload the full container — the MP4, MKV, or transport stream that holds both the AVS video and the audio — to the matching tool below.

If you are not sure whether your file is a bare stream or a container, check the extension and how it plays: a raw .cavs cannot be opened by ordinary media players at all, while .mp4, .mkv, and .ts can carry both video and audio together and play in normal software.

Where Your Audio Probably Is

• The original playable file: if you ever watched this footage with sound, that source was almost certainly a container — an MP4, MKV, or transport stream — not the bare .cavs. Convert that file, not the demuxed stream.
• An MP4 container: use MP4 to M4A to copy or re-encode the audio track from an MP4 (which can wrap AVS video alongside an audio track) into an M4A.
• An MKV or transport stream: use MKV to M4A for Matroska files, or TS to M4A for the MPEG transport streams common in Chinese broadcast capture, both of which interleave video and audio.

When This Doesn't Work

If your CAVS file is a true elementary stream with no companion audio, no tool can manufacture sound that was never encoded — the fix is to find the original container or the separate audio file. And keep one thing in mind even when audio is present: broadcast and set-top audio is itself almost always a lossy codec such as AAC, MP2, or AC-3, so re-encoding it to the AAC inside an M4A is a lossy-to-lossy step. The converter preserves what it can, but a second lossy pass cannot restore detail the original encode already discarded — going to M4A is for compatibility, not a quality upgrade. If you only want the video in a playable package rather than its audio, transcode the raw stream with CAVS to MP4 to make it open in normal players, or use CAVS to WebM for a web-friendly container.

Frequently Asked Questions

Why is my CAVS to M4A output silent or empty?

Because a raw .cavs file is an AVS1 video elementary stream and holds no audio. There is no soundtrack inside the file to decode, so any M4A produced from a bare .cavs will be silent. The audio for that footage lived in the container — an MP4, MKV, or transport stream — that the video was demuxed from. Convert that container to M4A instead.

Does a .cavs file contain audio I can extract?

Normally no. CAVS, standardized in China as GB/T 20090.2-2006 (its Part 2 covers video), is a video specification, and a plain .cavs is a raw AVS video bitstream handled by FFmpeg's cavsvideo raw demuxer with no audio track. You only get sound out if the file you uploaded is actually a container (such as an MP4 misnamed .cavs) that happens to carry an audio track alongside the video.

Will M4A improve the quality of audio extracted from an AVS video?

No. M4A stores AAC, which is itself a lossy codec, and the audio paired with AVS broadcast video was also almost always lossy — AAC, MP2, or AC-3. Re-encoding one lossy source into the AAC inside an M4A is a lossy-to-lossy conversion: it produces a widely compatible file but cannot recover detail the original encode already threw away. Choose M4A for playback on Apple and mobile devices, not as a fidelity upgrade.

How do I get M4A audio from an AVS source that actually has sound?

Start from a file that genuinely contains an audio track. If you have an MP4, use MP4 to M4A; for a Matroska file use MKV to M4A; for an MPEG transport stream use TS to M4A. All three interleave video and audio, so the converter has a real audio track to decode into the AAC of an M4A. A bare .cavs stream does not.

What is the difference between an M4A and an MP4 from the same source?

Both are MPEG-4 containers, but an M4A holds audio only — just the AAC track — while an MP4 carries the video alongside it. From a CAVS source that actually has sound, choose M4A when you want the soundtrack on its own (for a music player or podcast app) and MP4 when you want the picture and audio together. The audio bytes inside each are AAC either way.

Is this CAVS converter free, and how is my file handled?

Yes. There is no sign-up and no watermark. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — never shared or made public.