Turn old Windows Media Video files from Windows Movie Maker, screen recorders and camcorder software into MP4 files that play on iPhone, Mac, Android, smart TVs and every website. The ffmpeg engine runs inside your browser, so your videos never leave your computer.
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MP4 settings
Best quality, bigger fileSmaller file
Files
No files yet. Add one or more WMV videos above; their codec, resolution, length and audio are read instantly from the file header.
Preview
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How to use the WMV to MP4
Add your WMV files by dropping them on the box or clicking Choose WMV files. The codec, resolution and length appear right away.
Set the quality slider: CRF 23 is a good balance; move left for higher quality or right for a smaller file.
Choose a resolution: keep the original, or downscale large videos to 720p for faster conversion and smaller files.
Press Convert to MP4. The first time, the converter (about 31 MB) is downloaded and cached by your browser. Watch the progress bar.
Preview the MP4 in the player and press Download MP4, or Download all (ZIP) for several files.
What's inside a WMV file?
WMV files use Microsoft's Advanced Systems Format (ASF) container, the same one used for .asf and .wma files. Inside are video encoded with one of the Windows Media Video codecs and, usually, Windows Media Audio. These codecs were the default for Windows Movie Maker, Windows Media Encoder, many screen recorders and camcorder software from roughly 1999 to 2012. Modern phones, Macs and websites expect H.264 video and AAC audio in an MP4 container, which is why WMV files often refuse to play or upload today. When you add a file, the tool reads its ASF header and shows which codecs it uses.
Codec in the WMV
FourCC / tag
Typical source
WMV 7
WMV1
Windows Media Player 7 era, early web video
WMV 8
WMV2
Early Windows Movie Maker versions, early-2000s downloads
WMV 9 (Main profile)
WMV3
Windows Movie Maker on XP/Vista/7, most WMV files
VC-1 / WMV 9 Advanced
WVC1, WMVA
HD WMV, Xbox captures, some Blu-ray extracts
Windows Media Screen
MSS1, MSS2
Screen recordings and tutorials
WMA 2, WMA Pro, WMA Lossless, WMA Voice
0x161, 0x162, 0x163, 0x0A
Audio track; converted to AAC
Choosing the quality and size
The slider is the x264 Constant Rate Factor. Unlike a fixed bitrate, CRF keeps the visual quality steady and lets the file size follow the content: a static screen recording becomes tiny, while fast action needs more data. Practical starting points:
CRF 18-20: archiving family videos or anything you may edit later.
CRF 23 (default): general use, sharing and uploading.
CRF 26-28: screen recordings, lectures and email attachments.
CRF 30+: only when size matters more than detail.
Many WMV files from the 2000s are 320×240 or 640×480, so there is nothing to gain from upscaling; keep the original resolution. For HD WMV, downscaling to 720p shortens the conversion considerably because the encoder runs on a single CPU thread in the browser. Turn on Deinterlace only if moving edges show comb-like horizontal lines, which happens with TV and DV camcorder captures.
The exact conversion
The tool runs the equivalent of ffmpeg -i input.wmv -c:v libx264 -preset veryfast -crf 23 -pix_fmt yuv420p -profile:v high -c:a aac -b:a 128k -ac 2 -movflags +faststart output.mp4 with your chosen values. Odd frame sizes are rounded to even numbers (required by H.264 4:2:0), non-square pixels are converted to square pixels, and the fast-start flag moves the index to the front of the file so the MP4 starts playing immediately when streamed.
Frequently asked questions
How do I convert WMV to MP4 for free?
Drop the WMV file on this page, keep the default quality (CRF 23) and press Convert to MP4. The video is re-encoded to H.264 with AAC audio inside your browser and you can preview and download the MP4 when the progress bar finishes. There is no watermark, sign-up or file upload.
Why can't WMV just be copied into MP4 without re-encoding?
WMV files use Microsoft's Windows Media Video codecs (WMV 7, 8, 9 or VC-1) and Windows Media Audio. MP4 players such as iPhones, Macs, Android and web browsers do not decode those codecs, so the picture has to be re-encoded to H.264 and the sound to AAC. A remux would produce a file that most devices still can't play.
Will converting WMV to MP4 lose quality?
Re-encoding always changes the data, but at CRF 18 to 21 the result is visually indistinguishable from the WMV for almost everyone. H.264 is more efficient than the WMV codecs, so the MP4 is often smaller than the original at the same visible quality.
What does the CRF quality slider mean?
CRF (Constant Rate Factor) is the x264 encoder's quality setting. Lower numbers mean higher quality and bigger files; 23 is the encoder's default. As a rule of thumb, raising CRF by 6 roughly halves the file size and lowering it by 6 roughly doubles it.
Can it convert DRM-protected WMV files?
No. Videos bought or rented through old Windows Media DRM stores are encrypted, and no converter can decode them without the license. The tool detects the DRM header and tells you instead of failing silently.
Is my video uploaded to a server?
No. The converter is ffmpeg compiled to WebAssembly and runs in your browser tab. The WMV is read from your disk and the MP4 is created in memory on your own computer.
Is there a file size limit?
The practical limit is the memory available to a browser tab. Files up to a few hundred megabytes convert comfortably on most computers; the tool refuses files over about 1.9 GB. Downscaling to 720p reduces memory use and speeds up long HD recordings.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.