WEBM File Format (.webm)

A WEBM file holds VP8, VP9 or AV1 video with Vorbis or Opus audio in a cut-down version of the Matroska container, restricted to codecs that carry no patent licensing so browsers can play them freely.

.webmVideo Files

WEBM at a glance#

Full name	WebM
File extension	.webm
Category	Video Files
Developer	Google
First released	2010
MIME types	video/webmaudio/webm
Compression	Lossy
Specification	WebM Container Guidelines
FileFlip support	FileFlip reads and writes this format

What a .webm file can hold#

These are the things a WEBM file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Transparency (alpha channel)	Yes
Embedded metadata	Yes
Audio	Yes
Video	Yes
Subtitle tracks	No
Streaming	Yes

Strengths and limitations of WEBM#

What WEBM does well

No patent licence to negotiate or pay, which is the whole reason the format exists
Plays in Chrome, Firefox and Edge with nothing installed, and has since 2010
YouTube serves VP9 with Opus audio in WebM over DASH, including its 4K streams
VP9 holds more detail than H.264 at the same bitrate, so pages get lighter
VP9 in WebM can carry an alpha channel, so video sits over a page with real transparency

Where WEBM falls short

Safari only reached full support in version 16 on macOS and iOS 17.4, so older Apple devices show nothing
Final Cut Pro does not list WebM among the formats it reads, and most editing software wants a plugin at best
Only a short list of codecs is legal inside, so H.264 video has to be re-encoded to get in
Smart TVs, consoles and set-top boxes largely ignore the format

Choose WebM when the video is going on a web page and you want it to play in browsers without a codec licence attached to it.

Convert WebM to MP4 when the file has to leave the browser, whether that is an edit timeline, an older iPhone or a television.

How to open a .webm file#

A .webm file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts WEBM into a format your machine already opens, and it does it in the browser tab rather than on a server.

Platform	Programs that open it
Windows	VLC, mpv, MPC-HC
macOS	VLC, IINA, mpv
Linux	VLC, mpv, GNOME Videos
iOS	VLC, Safari on iOS 17.4 and later
Android	Chrome, VLC, MX Player
Web	Chrome, Firefox, Edge, Safari 16 and later, FileFlip

WEBM questions people ask#

Why did my screen recording save as a WEBM file?

Browser-based recorders and screen capture tools save WEBM because it is what the browser can encode without licensing anything. Recording in the browser goes through the MediaRecorder API, and VP8 or VP9 in WebM is the combination browsers ship by default, since encoding H.264 would mean paying for the patents. The recording is fine, it just needs converting before most editing software will take it.

What is the difference between WebM and MKV?

WebM is a deliberately narrowed version of Matroska. It uses the same container structure but only allows VP8, VP9 or AV1 video with Vorbis or Opus audio, where MKV takes any codec at all. That restriction is the point: a browser can support WebM completely, whereas supporting MKV would mean supporting every codec ever put in one.

Does converting WebM to MP4 lose quality?

Converting WebM to MP4 usually re-encodes the video and loses a little quality, because the VP9 or VP8 inside a WebM is not what MP4 players expect to find. MP4 can technically carry VP9 and AV1 now, but almost nothing in the wild plays those from an MP4, so a real conversion means encoding to H.264. Going the other way, MP4 to WebM, always re-encodes too, since H.264 is not allowed inside WebM at all.

Can WebM video have a transparent background?

WebM is one of the few video formats that carries transparency, using an alpha channel alongside VP9. That makes it the usual way to put video over a web page without a rectangular black box around it. The transparency does not survive conversion to MP4, since H.264 in MP4 has no alpha channel to put it in.

Does WebM play on iPhone?

WebM plays on recent iPhones and not on older ones. Safari had no WebM support for years, gained partial support along the way, and only reached full support in Safari 16 on macOS and iOS 17.4 on the phone. Anything older shows an empty player. VLC for iOS plays WebM regardless of the iOS version, and converting to MP4 avoids the question entirely.

Converting WEBM files#

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.