Convert CAVS to WMV — Free Online Tool
Convert CAVS (Chinese Audio Video Standard) files to WMV using Microsoft's MPEG-4 video codec and WMA audio, making Chinese broadcast content compatible with Windows Media Player and legacy Windows-based systems. This tool re-encodes the video through the msmpeg4 codec and wraps everything in ASF (Advanced Systems Format), the underlying container for WMV.
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 video codec that has virtually no support outside specialized Chinese broadcast software. During this conversion, FFmpeg decodes the CAVS video stream from scratch and re-encodes it using Microsoft's MPEG-4 v3 (msmpeg4) codec — there is no stream copying possible here since the codecs are entirely incompatible. The AAC audio track from the CAVS file is similarly decoded and re-encoded into WMA v2 (wmav2), Microsoft's native audio codec for WMV. The output is wrapped in an ASF container (triggered by the -f asf flag), which is the binary format that WMV files actually use. Because both video and audio are fully re-encoded, this is a computationally intensive conversion that will take longer than a simple remux, and involves two generations of lossy compression.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg application, the open-source multimedia processing engine that powers this conversion both in the browser (via FFmpeg.wasm) and on the desktop command line. |
-i input.cavs
|
Specifies the input CAVS file. FFmpeg will detect the Chinese Audio Video Standard video codec and the associated audio stream for decoding prior to re-encoding into WMV. |
-c:v msmpeg4
|
Selects Microsoft MPEG-4 version 3 as the video encoder, which is the native video codec for WMV files and ensures compatibility with Windows Media Player and legacy Windows media software. |
-c:a wmav2
|
Sets Windows Media Audio v2 as the audio codec, replacing the AAC audio from the CAVS source with Microsoft's proprietary lossy audio format that WMV containers are designed to use. |
-b:v 2000k
|
Sets the video bitrate to 2000 kilobits per second for the msmpeg4 encoder. Unlike the CRF quality scale used in CAVS encoding, WMV uses constant bitrate control, and 2000k is a reasonable default for standard-definition to moderate HD content. |
-b:a 128k
|
Sets the WMA v2 audio bitrate to 128 kilobits per second, matching the default audio quality from the CAVS source and providing a good balance between file size and audio fidelity. |
-f asf
|
Forces FFmpeg to use the ASF (Advanced Systems Format) container muxer, which is the actual binary format of WMV files. This flag is required because FFmpeg needs explicit instruction to use ASF muxing with the msmpeg4 codec, ensuring the .wmv output file is correctly structured and playable. |
output.wmv
|
The name of the resulting WMV file. The .wmv extension signals to Windows and media players that this is a Windows Media Video file using the ASF container, compatible with Windows Media Player and other WMV-supporting software. |
Common Use Cases
- Playing Chinese broadcast recordings or IPTV captures on a Windows PC that only has Windows Media Player installed and lacks CAVS codec support
- Archiving legacy Chinese digital television content into a more universally readable format for long-term storage on Windows-centric media servers
- Preparing CAVS-encoded footage for editing in older versions of Windows Movie Maker or other legacy Microsoft video tools that support WMV but not CAVS
- Distributing Chinese-standard video content to colleagues or clients whose Windows systems have not installed any third-party codec packs
- Embedding video into older Microsoft Office presentations or SharePoint environments that natively support WMV/ASF playback
- Transcoding CAVS broadcast captures for streaming through Windows Media Services on enterprise Windows Server deployments
Frequently Asked Questions
Yes, because both the input (CAVS) and output (WMV with msmpeg4) are lossy formats, this conversion involves double lossy compression — the video is decoded from its original CAVS quality and then re-encoded at 2000k bitrate using Microsoft's MPEG-4 v3 codec. The msmpeg4 codec is significantly older and less efficient than modern codecs like H.264, so at equivalent bitrates it will generally produce softer, more compressed-looking video than the source. For best results, increase the -b:v value (e.g., to 4000k or 6000k) if file size permits.
WMV is not a true standalone container format — it is actually Microsoft's Advanced Systems Format (ASF) with a .wmv file extension. FFmpeg needs the explicit '-f asf' flag to force ASF container muxing because it doesn't always infer this correctly from the .wmv extension when using the msmpeg4 video codec. Without this flag, the output file may be unplayable or improperly formatted even if it carries the .wmv name.
Yes, that is the primary goal of this conversion. The msmpeg4 video codec and wmav2 audio codec are natively supported by Windows Media Player on all modern Windows versions without requiring any additional codec packs. The ASF container is Microsoft's own format, so compatibility with WMP, Windows Explorer thumbnail previews, and other Windows media infrastructure is as strong as possible.
WMV uses constant bitrate (CBR) encoding controlled by the -b:v flag, unlike the CRF-based quality control used in CAVS source encoding. To increase video quality, raise the -b:v value — for example, replace '-b:v 2000k' with '-b:v 4000k' or '-b:v 6000k'. For audio quality, adjust '-b:a' from the default 128k up to 192k or 256k. Note that unlike CRF encoding, higher bitrate does not guarantee better perceived quality if the source CAVS footage itself was encoded at low quality.
Yes, on the command line you can use a shell loop to process multiple files. On Linux or macOS: 'for f in *.cavs; do ffmpeg -i "$f" -c:v msmpeg4 -c:a wmav2 -b:v 2000k -b:a 128k -f asf "${f%.cavs}.wmv"; done'. On Windows Command Prompt: 'for %f in (*.cavs) do ffmpeg -i "%f" -c:v msmpeg4 -c:a wmav2 -b:v 2000k -b:a 128k -f asf "%~nf.wmv"'. This browser-based tool processes one file at a time.
Generally no. CAVS is a Chinese broadcast standard with its own metadata structures that do not map directly to ASF/WMV container metadata fields. FFmpeg will attempt to carry over basic tags if present, but broadcast-specific CAVS metadata (such as program guide information or Chinese DTV service identifiers) will be lost in the conversion. The WMV file will contain standard ASF metadata fields only, and likely just the filename-derived title at most.
Technical Notes
The msmpeg4 codec used for WMV output is Microsoft's older MPEG-4 Part 2 implementation (specifically version 3, sometimes called MS-MPEG4v3 or DivX predecessor), which predates modern codecs by nearly two decades. It is considerably less compression-efficient than CAVS or H.264, meaning a WMV file at 2000k bitrate may look worse than the original CAVS file at a lower bitrate. The wmav2 audio codec is Windows Media Audio version 2, a proprietary Microsoft lossy codec competitive with MP3 at similar bitrates but not as efficient as AAC. Chapters, subtitles, and multiple audio tracks from any CAVS source are not preserved — WMV as implemented here carries a single video and single audio stream only. The ASF container does technically support DRM (Digital Rights Management), but this tool outputs unprotected, unencrypted WMV files. File sizes will typically be larger than the source CAVS file at the default 2000k video bitrate, especially for lower-bitrate CAVS broadcasts. If you need WMV for a specific legacy application, test playback before committing to a large batch conversion, as msmpeg4 compatibility can vary between software versions.