Convert CAVS to M4V — Free Online Tool
Convert CAVS (Chinese Audio Video Standard) files to Apple M4V format, re-encoding the video with H.264 (libx264) and audio with AAC — producing iTunes-compatible files optimized for iOS devices, Apple TV, and web streaming. This is a full transcode from a Chinese broadcast standard into Apple's MPEG-4 container.
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 video codec (AVS Video) that is not natively supported by Apple devices or iTunes. This conversion performs a full re-encode: the AVS video stream is decoded and re-encoded using H.264 (libx264), while the audio is transcoded to AAC at 128k bitrate. The output is wrapped in Apple's M4V container — a variant of MPEG-4 Part 14 — with the -movflags +faststart flag applied, which moves the MP4 index (moov atom) to the beginning of the file. This makes the M4V suitable for progressive web streaming and direct playback in iTunes or on iOS/tvOS devices without buffering the entire file first.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In this browser-based tool, FFmpeg runs as a WebAssembly (WASM) module locally in your browser — no file data is sent to any server. The same command works identically on a desktop FFmpeg installation for files over 1GB. |
-i input.cavs
|
Specifies the input file in CAVS format. FFmpeg will use its built-in AVS decoder to demux and decode the proprietary Chinese AVS Video stream and accompanying audio from this file. |
-c:v libx264
|
Re-encodes the video stream using the H.264 encoder (libx264). Since CAVS's native AVS Video codec is not compatible with Apple's M4V container or Apple devices, a full transcode to H.264 is required — this is not a simple stream copy. |
-c:a aac
|
Transcodes the audio stream to AAC using FFmpeg's built-in AAC encoder. AAC is the native and preferred audio codec for the M4V container and is required for iTunes and iOS compatibility. |
-crf 23
|
Sets the H.264 Constant Rate Factor to 23, the libx264 default. This controls video quality: lower values (e.g., 18) produce higher quality at larger file sizes, while higher values (e.g., 28) compress more aggressively. CRF 23 is a balanced starting point for CAVS broadcast content. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, which delivers transparent quality for stereo audio typical of CAVS broadcast content and keeps file sizes reasonable for iTunes library storage. |
-movflags +faststart
|
Moves the MP4/M4V moov atom (the file index) to the beginning of the output file after encoding completes. This is essential for web streaming and Apple TV playback, allowing the M4V to begin playing before the entire file is downloaded. |
output.m4v
|
Defines the output filename with the .m4v extension. The M4V extension signals to iTunes, QuickTime, and Apple devices that this is an Apple-formatted MPEG-4 video file, enabling correct association and playback behavior across the Apple ecosystem. |
Common Use Cases
- Making Chinese broadcast or satellite recordings in CAVS format playable on an iPhone, iPad, or Apple TV without conversion errors or blank video screens.
- Importing CAVS footage captured from Chinese digital TV tuner cards into iTunes or the Apple TV app for personal media libraries.
- Preparing CAVS source material for upload to platforms that require H.264/AAC in an MP4-family container, such as Apple Podcasts video or Apple's Transporter tool.
- Archiving Chinese-standard broadcast content in a universally compatible format that will remain playable on Western hardware and software for years to come.
- Sending CAVS video clips to colleagues or clients who use macOS or iOS and cannot play back AVS-encoded content natively.
- Embedding CAVS-sourced video into a website or iOS app by converting to M4V with faststart enabled for smooth in-browser or in-app streaming.
Frequently Asked Questions
Yes — this is a lossy-to-lossy transcode. The AVS video codec in the CAVS file must be fully decoded and re-encoded into H.264, which introduces a second generation of compression loss. The default CRF value of 23 produces good visual quality for most content, but if your source CAVS file was already heavily compressed, some additional quality degradation is unavoidable. For highest fidelity, lower the CRF value (e.g., to 18) to give H.264 more bitrate budget during encoding.
CAVS uses the AVS (Audio Video Standard) video codec, a Chinese national standard developed independently of H.264 and HEVC. Apple's hardware decoders and QuickTime/AVFoundation framework only support a specific set of codecs — primarily H.264, HEVC, ProRes, and a few others. AVS is not among them, so iPhones, iPads, Macs, and Apple TVs will either refuse to play CAVS files entirely or display a black screen with audio only. Converting to M4V with H.264 resolves this completely.
MP4-family files (including M4V) store a metadata index called the 'moov atom' that a player needs to begin playback. By default, FFmpeg writes this atom at the end of the file after encoding is complete. The +faststart flag runs a post-processing step that relocates the moov atom to the beginning of the file, so a browser or streaming player can start rendering the video after downloading only a small portion of the file rather than waiting for the entire download. This is critical for web embedding and Apple's HTTP streaming stack.
Yes — M4V supports HEVC (libx265), and you can substitute it in the FFmpeg command by replacing '-c:v libx264' with '-c:v libx265'. HEVC typically achieves the same visual quality at roughly half the file size compared to H.264 at the same CRF. However, HEVC M4V files have slightly narrower compatibility: older Apple devices (pre-2017) and some third-party software may not support them. For maximum device compatibility, H.264 remains the safer default choice.
Adjust the CRF value passed to the -crf flag. CRF (Constant Rate Factor) controls quality on a scale from 0 (lossless) to 51 (worst quality), with 23 as the default. Lower numbers mean better quality and larger file sizes — CRF 18 is often described as 'visually lossless' for H.264. For example, to convert a CAVS file to high-quality M4V, change the command to: ffmpeg -i input.cavs -c:v libx264 -c:a aac -crf 18 -b:a 128k -movflags +faststart output.m4v
The CAVS format does not carry subtitle or chapter metadata, so there is nothing to transfer even though M4V natively supports both. If you need to add subtitles to the resulting M4V, you would need to provide a separate subtitle file (e.g., .srt or .ass) and include it in the FFmpeg command with '-c:s mov_text'. Chapters would similarly need to be added via metadata injection after conversion. The conversion itself will not produce a file with embedded subtitles or chapters.
Technical Notes
CAVS (Chinese Audio Video Standard, also known as AVS1) is a codec-plus-container format used primarily in Chinese digital broadcasting and optical disc applications. Its video codec, AVS Video (Part 2), is broadly comparable in compression efficiency to H.264 but is implemented in dedicated hardware decoders used in Chinese set-top boxes and Blu-ray players — hardware that is rarely found outside China. FFmpeg can decode CAVS video via its built-in AVS decoder, making this conversion possible entirely in software. Because both the input and output formats are lossy, the conversion incurs two rounds of compression artifacts, making CRF tuning particularly important for quality-sensitive material. The M4V container is functionally identical to .mp4 with the extension indicating iTunes association; the -movflags +faststart optimization is applied automatically by this tool and is especially valuable for any M4V intended for web delivery. Note that M4V's DRM capability (Apple FairPlay) is not used or applied during this conversion — the output is a standard, unprotected file. CAVS files do not contain subtitle or chapter data, so the M4V output will lack these tracks; multiple audio track support is also absent from CAVS, so only a single audio stream will be present in the output.