Compress WMA Online — Free File Size Reducer
Compress a WMA file by re-encoding it with the WMA v2 codec at a lower bitrate, reducing file size while keeping it in the native Windows Media Audio format. This is useful when you need smaller WMA files for streaming or storage without changing the container or codec.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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
Because both the input and output are WMA files using the wmav2 codec, this tool performs a full audio re-encode rather than a simple remux. FFmpeg decodes the original WMA audio stream, then re-encodes it at the target bitrate (default 128k) using the wmav2 encoder. Since WMA is a lossy format, this is a lossy-to-lossy transcode — each encode cycle introduces a small amount of additional quality degradation. The benefit is a meaningfully smaller file size, which is the primary goal of compression. Metadata tags embedded in the original WMA file are preserved through the process.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles all decoding, encoding, and container operations. In the browser version, this runs via FFmpeg.wasm compiled to WebAssembly, so no files leave your machine. |
-i input.wma
|
Specifies the input WMA file. FFmpeg reads the ASF container and identifies the audio stream encoded with wmav1 or wmav2, then decodes it to raw PCM audio for re-encoding. |
-c:a wmav2
|
Sets the audio encoder to wmav2 (Windows Media Audio v2), the standard and improved WMA codec. This ensures the output remains a proper WMA file compatible with Windows Media Player and WMA-capable devices, as opposed to the older and lower-quality wmav1. |
-b:a 128k
|
Sets the audio bitrate of the output WMA stream to 128 kilobits per second. This is the target compression level — lower than typical high-quality WMA files (256k–320k), it reduces file size significantly while maintaining acceptable audio quality for music and voice. |
output.wma
|
Defines the output filename with the .wma extension, telling FFmpeg to write the re-encoded audio into an ASF/WMA container. The resulting file is a standard WMA file at the specified lower bitrate. |
Common Use Cases
- Reducing the size of a large WMA music library to fit on a device with limited storage, such as an older Windows Phone or portable media player that only supports WMA playback
- Compressing WMA audio files before uploading them to a Windows Media Services streaming server, where lower bitrates reduce bandwidth consumption for listeners
- Shrinking WMA audiobook or podcast files that were originally recorded or distributed at a high bitrate (256k or 320k) down to a more practical size for everyday listening
- Preparing WMA files for email attachment or file transfer where size limits apply, by reducing a high-bitrate WMA to 96k or 64k
- Archiving or batch-downsizing a collection of WMA files received from legacy Windows Media Player or Windows Media Center recordings
- Lowering the bitrate of WMA files used as background audio in Windows-based kiosk or presentation systems where storage is constrained
Frequently Asked Questions
Yes. WMA is a lossy format, so the original file already discards some audio information during its first encode. Re-encoding to a lower bitrate with wmav2 introduces another round of lossy compression, permanently reducing quality further. The degradation is typically subtle when stepping down moderately (e.g., from 192k to 128k), but becomes more noticeable at very low bitrates like 64k. This quality loss cannot be reversed, so keep a copy of the original if the source quality matters.
WMA v1 (wmav1) is the original Windows Media Audio codec introduced with early versions of Windows Media Player and is considered largely obsolete. WMA v2 (wmav2) is its successor, offering better audio quality at the same bitrate through improved psychoacoustic encoding. This tool uses wmav2 as the output codec, which is also the most common codec found in modern WMA files and is the default used by Windows Media Player for encoding.
File size reduction depends on the bitrate difference between the original and the target. For example, compressing from 320k to 128k reduces the encoded audio data by approximately 60%, leading to a proportionally smaller file. The actual file size savings may be slightly less than the bitrate ratio suggests due to fixed overhead from the WMA container headers and metadata, but for long audio files (several minutes or more) the savings closely track the bitrate reduction percentage.
Yes. FFmpeg preserves the metadata tags embedded in the WMA container (such as artist, album, title, and track number) when re-encoding to a new WMA file. These tags are stored at the container level in the ASF (Advanced Systems Format) wrapper that WMA uses, and FFmpeg copies them to the output file automatically during the transcode.
Replace the value after -b:a in the command with your desired bitrate. For example, to compress more aggressively, use -b:a 64k or -b:a 96k. For lighter compression that preserves more quality, use -b:a 192k or -b:a 256k. The full command would look like: ffmpeg -i input.wma -c:a wmav2 -b:a 96k output.wma. Bitrates below 64k are not recommended for wmav2 as audio quality degrades severely.
FFmpeg itself processes one file at a time, but you can batch process multiple WMA files using a shell loop. On Linux or macOS, use: for f in *.wma; do ffmpeg -i "$f" -c:a wmav2 -b:a 128k "compressed_$f"; done. On Windows Command Prompt, use: for %f in (*.wma) do ffmpeg -i "%f" -c:a wmav2 -b:a 128k "compressed_%f". This applies the same compression settings to every WMA file in the current directory.
Technical Notes
WMA files use the ASF (Advanced Systems Format) container developed by Microsoft, which supports metadata tags and DRM (Digital Rights Management) protection. This tool re-encodes using the wmav2 codec, which operates as a transform-based perceptual audio coder similar in architecture to AAC and Vorbis. One important limitation: if your source WMA file has DRM protection applied, FFmpeg cannot decode it and the conversion will fail — DRM-protected WMA files require licensed Microsoft software to decode. The wmav2 encoder in FFmpeg is an open-source implementation that is broadly compatible with Microsoft's own decoder, meaning output files will play correctly in Windows Media Player, VLC, and most WMA-compatible devices. Since both input and output are lossy, users should choose the lowest bitrate that still meets their quality requirements and avoid repeated re-encodes of the same file, as each generation degrades quality. The ASF container metadata (ID3-style tags) is preserved automatically during the transcode.