MyMediaTools

Convert CAVS to MP4 — Free Online Tool

Convert CAVS (Chinese Audio Video Standard) files to MP4 using H.264 video and AAC audio encoding. This tool makes CAVS content — a Chinese broadcast-standard format with limited international player support — universally playable on any modern device or platform.

FFmpeg Command

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Estimated output:

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How It Works

CAVS files use the AVS1 video codec, a Chinese national standard that is rarely supported outside of dedicated Chinese media hardware and software. During this conversion, the AVS1 video stream must be fully decoded and re-encoded to H.264 (libx264), and the audio is re-encoded to AAC at 128k. There is no stream-copy shortcut here — both video and audio undergo a full transcode. The output is wrapped in an MP4 container with the -movflags +faststart flag, which relocates the MP4 index (moov atom) to the beginning of the file so it can begin playing before fully downloading, making it suitable for web streaming.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg command-line tool. When run locally on your desktop, this must be installed on your system; in this browser-based tool, it runs via FFmpeg.wasm compiled to WebAssembly.
-i input.cavs Specifies the input file in CAVS format. FFmpeg will invoke its AVS1 video decoder and the appropriate audio decoder to read the Chinese-standard encoded content from this file.
-c:v libx264 Re-encodes the AVS1 video stream using the libx264 H.264 encoder. Since AVS1 and H.264 are entirely different codecs, a full video decode and re-encode is required — there is no copy option available for this conversion.
-c:a aac Re-encodes the audio stream to AAC using FFmpeg's native AAC encoder. The audio from the CAVS source (which may use a Chinese-standard audio codec) is fully transcoded to AAC, which is the standard audio codec in MP4 files and is natively supported across all modern browsers and devices.
-crf 23 Sets the Constant Rate Factor for libx264 to 23, the default quality level. This controls the trade-off between output file size and visual quality during the AVS1-to-H.264 transcode — lower values like 18 produce better quality at larger sizes, while higher values like 28 shrink the file at the cost of visible quality degradation.
-b:a 128k Sets the AAC audio bitrate to 128 kilobits per second. For typical CAVS broadcast audio content (speech, mono or stereo), 128k AAC delivers clean, transparent quality and is the standard bitrate for web and streaming delivery.
-movflags +faststart Moves the MP4 moov atom (the file's index and metadata) from the end to the beginning of the output file. This is critical if the converted MP4 will be streamed or embedded on the web, as it allows playback to begin before the entire file has loaded.
output.mp4 Specifies the output filename and container format. The .mp4 extension tells FFmpeg to write an MPEG-4 Part 14 container, which holds the newly encoded H.264 video and AAC audio tracks produced from the CAVS source.

Common Use Cases

  • Playing Chinese broadcast or IPTV recordings on devices that don't support the AVS1 codec, such as iPhones, smart TVs from non-Chinese brands, or media players like VLC on older systems.
  • Uploading CAVS video content to platforms like YouTube, Vimeo, or WeChat Video, which require widely compatible formats like MP4 with H.264.
  • Archiving Chinese digital TV recordings in a format that will remain playable long-term without relying on niche AVS1-capable software.
  • Editing CAVS footage in video editing software such as Adobe Premiere Pro or DaVinci Resolve, which do not natively support the AVS1 codec.
  • Sharing clips from Chinese broadcast content with international audiences who lack any AVS1-compatible playback infrastructure.
  • Embedding CAVS-sourced video into websites or apps where universal browser compatibility via the HTML5 video element is required.

Frequently Asked Questions

CAVS uses the AVS1 (Audio Video Standard) codec, a Chinese national standard developed primarily for domestic broadcast and hardware. It was designed for the Chinese market and is supported natively only by specific Chinese-manufactured set-top boxes, TVs, and a handful of software players. International operating systems, browsers, and media players almost universally lack built-in AVS1 decoding support, which is why converting to MP4 with H.264 is the practical solution for cross-platform playback.
Yes — this conversion involves a full re-encode of both video and audio, so some generation loss is unavoidable. The default CRF value of 23 for libx264 produces visually good quality for most content, but the degree of visible degradation depends heavily on the quality of the source CAVS file. If the CAVS source was already encoded at a low bitrate for broadcast efficiency, the MP4 output will reflect that baseline quality. Using a lower CRF value (e.g., 18) will produce a higher-quality output at the cost of a larger file size.
The CAVS format does not support embedded subtitle tracks or chapter markers, so there is nothing to carry over during conversion. The output MP4 container does support subtitles and chapters, but you would need to add them separately after conversion using a tool like FFmpeg or a video editing application.
Change the -crf value in the command to control H.264 quality. CRF (Constant Rate Factor) works on a scale where lower numbers mean higher quality and larger file sizes. The default of 23 is a good general-purpose setting. For archival or high-quality output, use -crf 18; for smaller files where some quality loss is acceptable, try -crf 28. For example: ffmpeg -i input.cavs -c:v libx264 -c:a aac -crf 18 -b:a 128k -movflags +faststart output.mp4.
Yes. On Linux or macOS, you can loop over all CAVS files in a directory with: for f in *.cavs; do ffmpeg -i "$f" -c:v libx264 -c:a aac -crf 23 -b:a 128k -movflags +faststart "${f%.cavs}.mp4"; 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.mp4". This is especially useful for converting a batch of recorded Chinese broadcast files in one operation.
Because CAVS uses the AVS1 codec, both the video decode and H.264 re-encode steps must be performed in software — there is no hardware acceleration path for AVS1 decoding in mainstream consumer hardware outside of specific Chinese chipsets. Contrast this with converting MP4 to MP4 where codec-compatible streams can be copied without re-encoding. The full software transcode of AVS1 to H.264 is computationally intensive, and processing time scales with the file's resolution and duration.

Technical Notes

CAVS (also called AVS1 or AVS+) was standardized by the Audio Video Coding Standard Workgroup of China as a royalty-managed alternative to H.264/AVC for Chinese domestic broadcast. The video codec achieves compression efficiency broadly comparable to H.264 but uses a distinct technical specification, which means codec libraries must explicitly implement AVS1 decoding — FFmpeg does include an AVS1 decoder, enabling this conversion. The audio in CAVS files is typically encoded with a Chinese-standard audio codec (like AVS Audio or DRA), which FFmpeg also handles, transcoding it to AAC for the MP4 output. Because neither the video nor audio codecs overlap between CAVS and standard MP4, this is always a full transcode with no possibility of stream copying. The -movflags +faststart flag is particularly valuable for CAVS-sourced content being repurposed for online distribution, as it ensures the MP4's metadata is front-loaded for progressive download. Metadata such as timestamps and titles embedded in CAVS broadcast streams may not be preserved in the output MP4, and the CAVS format's lack of subtitle and chapter support means the output is a clean audio/video-only container unless additional tracks are manually muxed afterward.

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