This MP4 to WMV conversion does not run here
WMV is a legacy Microsoft format. A few old players still ask for it.
The browser tries to encode WMV. Support is incomplete, and the conversion often fails.
What to do instead
If it fails, send MP4 or AVI instead. Those are the formats current devices actually play.
The page that does work is mp4-to-avi.
Why MP4 to WMV is its own job
MP4 to WMV sits on this site because MP4 and WMV are not interchangeable, even when they look similar in a file list. WMV is a legacy Microsoft format. A few old players still ask for it. Phones, browsers, Instagram, YouTube, and WhatsApp all expect MP4. Old Windows Media files are converted to MP4 so they play anywhere else.
The browser tries to encode WMV. Support is incomplete, and the conversion often fails.
The MP4 file you already have
MP4 with H.264 video and AAC audio is the safest video file to share in 2026. Soft subtitles such as ASS or PGS, and extra audio languages, are awkward or dropped when a tool re-encodes.
Keep the original MP4. Treat every other container as a compatibility copy.
What a WMV result is for
The download has to be WMV, because that is the format the next step named. Old Windows Media files are converted to MP4 so they play anywhere else. When FFmpeg can read the WMV, you get a normal MP4.
A successful MP4 will not look better than the WMV. If it fails, export from a Windows app that still plays the file.
How to tell that MP4 to WMV worked
MP4 to WMV is worth using only when WMV is what the next step actually named. WMV is a legacy Microsoft format. A few old players still ask for it. What you get from MP4 to WMV: The browser tries to encode WMV. Support is incomplete, and the conversion often fails. Before you trust it: If it fails, send MP4 or AVI instead. Those are the formats current devices actually play. The file stays on your device. The first run downloads a converter, so keep this tab open. A phone runs out of memory on long files. A computer is the safer place for a big clip. A second pass rarely helps. If the first WMV file is rejected, read the error from the program that rejected it. Another conversion of a bad result usually makes the file worse, not more compatible. When you are done, you should still have the MP4 original and one WMV download that you have opened. If those two are the same kind of failure, this was the wrong tool and the page above is the place that says so. Video files hide the real problem inside the container. MP4 to WMV re-encodes on your device. It does not silently copy every audio language and every subtitle the way a desktop remux can. If you needed those extra tracks, this download is the wrong result even when the picture plays. Convert a one-minute piece before a full movie, and stay on the tab while the converter downloads the first time.
Here is the decision for MP4 to WMV. You start with MP4 and you stop when a real program accepts WMV. If the other person can open only one video format, MP4 is that format. Some old WMV codecs cannot be read in the browser, and the conversion then fails. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
If it fails, send MP4 or AVI instead. Those are the formats current devices actually play.
A related step, if you still need one, is WMV to MP4.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.