Manatee

How to convert WMV to MP4 on a Mac

· 6 min read

Nothing built into macOS opens a WMV, so converting is the only way to watch or share one without installing a third-party player. Manatee converts WMV to MP4 in one drop: open it, choose Convert, drop the file, pick MP4, and the result plays in QuickTime, on an iPhone, and in any browser. The conversion re-encodes the video, so choose a good quality setting, and be aware that WMVs protected with Windows DRM cannot be converted by anything.

Why a Mac will not play WMV

WMV is Windows Media Video, Microsoft’s format from the era of Windows Media Player. The file is an ASF container holding video compressed with one of the WMV codecs (WMV7, WMV8, WMV9, or its standardized version, VC-1) and audio compressed with WMA. None of these codecs are included in macOS. Apple has never shipped them, and the third-party components that once added WMV playback to QuickTime stopped working when 32-bit plug-ins were dropped in macOS Catalina.

So when you double-click a .wmv on a Mac, QuickTime Player reports that the file is not compatible, Quick Look shows a generic icon, and Finder’s Get Info may list the codec as “Windows Media Video” with nothing to play it. The file is usually perfectly fine. It is just written in a language the Mac does not speak. QuickTime says the file isn’t compatible covers how to tell a codec problem from actual damage.

The fix is to re-encode the video into H.264 or HEVC with AAC audio inside an MP4 container, which every Apple device and every browser can play.

Convert with Manatee

Manatee accepts .wmv and .asf as input and converts them to MP4 or MOV using the ffmpeg engine bundled inside the app, which includes decoders for every WMV and WMA variant. It runs on macOS 12 Monterey or later, on Apple silicon and Intel. The file never leaves your Mac.

  1. Open Manatee and choose Convert.
  2. Drop the WMV into the window. You can drop a folder of them; each one becomes a job in the list with its own progress.
  3. Choose MP4 as the target.
  4. Click Convert. The MP4 is written next to the original WMV, which is not modified. Conversion time depends on the length and resolution of the video; standard-definition clips, which most WMVs are, go quickly.

Once done, double-click the MP4 and it opens in QuickTime Player. Drag it to Photos, attach it to a message, or upload it anywhere.

Manatee converts the whole file as it is. It does not trim, crop, add subtitles, deinterlace, change the frame rate, or join several WMVs into one. If the WMV was interlaced (common for ones captured from TV or old camcorders), the MP4 will show the same comb-like lines on motion. If it was damaged, Convert may stop partway, and Manatee’s Repair mode is the next step; the result is reported honestly as Fixed, Partial, or Not fixable, and a new copy is always written alongside the original.

If you have ffmpeg installed

ffmpeg is not part of macOS, but if it is on your system:

ffmpeg -i video.wmv -c:v libx264 -crf 20 -preset medium -c:a aac -b:a 160k video.mp4

-crf 20 is a quality setting; lower numbers mean higher quality and larger files, and 18 to 23 is the sensible range. To deinterlace at the same time, add -vf yadif before -c:v. For a folder of files:

for f in *.wmv; do ffmpeg -i "$f" -c:v libx264 -crf 20 -c:a aac "${f%.wmv}.mp4"; done

What happens to the quality

There is no way to put WMV video into an MP4 without re-encoding, because MP4 does not carry the WMV codecs. That means the conversion is lossy: the video is decoded to raw frames and compressed again with H.264. At a reasonable quality setting, the new compression is far more efficient than WMV’s, so the MP4 often looks indistinguishable from the original while being about the same size or smaller.

What you cannot get back is anything the WMV already lost. A 640x480 WMV encoded at 1 Mbps in 2006 has soft edges, blocky shadows, and muffled audio, and the MP4 will have all of that too. Converting at a very high quality does not restore detail; it just preserves the artifacts faithfully.

Practical guidance:

  • Keep the original resolution. Upscaling makes the file larger, not sharper.
  • Keep the original frame rate. Old WMVs at 25 or 29.97 fps should stay there.
  • Do not convert twice. If you later need a smaller file for email or messaging, compress it from the WMV-derived MP4 once, rather than chaining conversions; why compressing a video twice makes it look worse explains the damage.
  • Keep the WMV until you have checked the MP4 all the way through.

WMVs that cannot be converted

DRM-protected files. Windows Media supported a rights-management system, and some purchased or corporate training videos from the 2000s are locked with it. A protected WMV cannot be decoded by any converter on any platform without the license that was issued to the original Windows PC. Manatee does not crack passwords or DRM, and neither does anything else that works. If a file came from a store or a company portal and fails in every converter with an error about decryption, that is why.

Files with unusual codecs. A few WMVs contain screen-capture codecs (MSS2, for example) or very early WMV7 video. ffmpeg, and therefore Manatee, decode most of these, but a handful of rare variants are unsupported everywhere.

Truncated downloads. An ASF container is reasonably tolerant of damage at the end, so a truncated WMV often converts up to the cut-off point. If the MP4 stops early, the source was incomplete. How to check whether a video file is corrupted on a Mac describes how to confirm it.

Zero-byte files. Nothing can be converted from nothing. Get a fresh copy from the source.

Questions

Can I convert WMV to MOV instead of MP4?

Yes. Manatee offers MOV as a target. For most purposes MP4 is the better choice because it is accepted by more services; MOV vs MP4 lays out the difference. Inside, both would contain the same H.264 video.

Will the audio convert too?

Yes. WMA audio is decoded and written as AAC in the MP4. Multi-channel WMA Pro tracks come through as well, though most players will downmix them to stereo.

The converted file is larger than the WMV. Is that normal?

It can be, especially for low-bitrate originals, because the converter encodes at a quality level that preserves everything in the source. If size matters, use Manatee’s Shrink mode on the MP4 afterward and name a target size in MB.

Is there a way to watch WMV on a Mac without converting?

Third-party media players with their own built-in codecs can play WMV directly. Converting still makes sense when you want to share, edit, or import the video into Photos.