Video to WebM for Faster, Leaner Playback

Q: Why is my WebM larger than the original MP4?

The default CRF of 23 aims for high quality, and phone MP4s are often already compressed efficiently. Raise CRF to around 31–35, pick a lower Resolution or reduce 60 fps to 30 fps. A resolution preset above the source size also inflates the file.

Converting a video to WebM with VP9, VP8 or AV1

Convert a video to the WebM container and choose compatible video and audio codecs. Adjust resolution, frame rate and quality or bitrate for the intended player. WebM can be useful for videos embedded on websites, but file size depends on the source and encoding settings. Test the exported file in the browser or application where it will be used.

Cost: Free to use. File size and usage limits apply.

How to convert a video to WebM

Upload one video
Drop an MP4, MOV, MKV, WebM, AVI, M4V, MPEG/MPG or OGV file of up to 200 MB, or pick a file you already used in another tool under Uploads. One video is converted per job.
Check the codecs
Under 1. Codecs, Video codec is set to vp9 and Audio codec to opus. That pair is the usual WebM combination for websites, so most people can leave it as it is.
Open Optional resize if you need it
The collapsed Optional resize card holds Resolution, FPS, CRF, Video bitrate and Audio bitrate. Resolution starts at Original, CRF at 23, and the empty fields keep the source frame rate and the encoder's default audio bitrate.
Convert, compare, download
Click Convert to WebM. The result plays in the preview and the result card shows its file size, so you can check whether it came out smaller than your original before you click Download. Continue editing keeps your settings for another attempt.

VP9, VP8 or AV1: which codec goes into the WebM

WebM is only the container. The picture inside is compressed with one of three codecs, and that choice decides file size, encoding time and which players can open the file.

vp9 (default)

The standard choice for WebM on the web. It needs noticeably fewer bits than VP8 for the same picture, plays in current Chrome, Firefox and Edge, and responds to CRF as expected.

vp8

The older WebM codec, for legacy players that can't decode VP9. It encodes fastest but needs more bits than VP9 for the same picture, so choose a lower CRF or a higher Video bitrate for HD footage.

av1

Can use fewer bits than VP8 or VP9 for a comparable picture; the actual file size depends on the source and settings. It is also the slowest: in our tests AV1 took about twice as long as VP9. Older phones and browsers may not decode it, so test on your target device.

copy

Repackages the video stream without re-encoding, but only if the source already uses VP8, VP9 or AV1, for example a WebM or an MKV with VP9. Any other source is re-encoded to VP9. Setting a resolution, FPS or video bitrate also switches copy to vp9.

Audio, size and quality settings

Everything except the two codec fields sits in Optional resize. Empty FPS, Width and Height fields keep the source values.

Audio codec: opus is the default; with Audio bitrate empty a stereo track gets 96 kbps and a mono track 64 kbps. vorbis is for older players. copy keeps Opus or Vorbis audio unchanged and converts anything else, such as AAC from an MP4, to Opus. none removes the sound.
Resolution: Original keeps the source size. The presets scale the video to a standard quality level while keeping its aspect ratio: 360p fits it into 640 × 360 px, 480p into 854 × 480 px, 720p into 1280 × 720 px, 1080p into 1920 × 1080 px, 1440p into 2560 × 1440 px and 4k into 3840 × 2160 px. A preset above the source size upscales, which adds size but no detail.
Width and Height (Custom): Choose Custom to enter pixels. Fill in only Width or only Height and the other side follows the aspect ratio: Width 720 turns a 1080 × 1920 px phone clip into 720 × 1280 px. Fill in both and the video is scaled to exactly that size, stretched if the proportions differ. Odd values are rounded down to an even number; the maximum is 7680 × 4320 px.
FPS: Empty keeps the source frame rate, including fractional rates such as 29.97 fps. Enter a value from 1 to 120 fps, for example 30 or 29.97. Going from 60 to 30 fps saves bits; a rate above the source only duplicates frames.
CRF: Constant quality from 0 to 63; lower means better quality and a larger file. The default 23 is a high-quality setting for VP9 and AV1 and can produce a WebM larger than your MP4. As a rule of thumb, 31–33 suits 720p and 1080p web video.
Video bitrate: A fixed average data rate for the picture instead of the CRF quality target. Type it with a unit, for example 2500k for 2,500 kbps or 4M for 4 Mbps. Useful when a player or platform expects a specific rate.
Audio bitrate: Also typed with a k suffix, such as 128k. As a rule of thumb, Opus sounds clean at 64 kbps for speech and around 128 kbps for music. It has no effect with copy or none.

Formats and limits

Input formats: MP4, MOV, MKV, WebM, AVI, M4V, MPEG/MPG, OGV
Output format: WebM with VP9, VP8 or AV1 video and Opus or Vorbis audio
Maximum file size: 200 MB per video
Files per job: 1
Tracks: One video track, one audio track and one text subtitle track (converted to WebVTT) are kept. Phone rotation is applied, so portrait clips come out upright.
Metadata: Tags such as title, recording device and GPS location are copied into the WebM. To remove them, use Compress Video, which strips metadata by default and can also output WebM.
Processing: On our servers with FFmpeg (libvpx, libaom and libopus encoders), in a single pass. A job can run for up to 15 minutes.
Watermark: None
Storage: Uploads and results are deleted automatically after 48 hours for guests and after 30 days for free accounts. Paid plans can keep files longer.

Frequently asked questions

Should I use VP9 or VP8 for WebM?

VP9 in almost every case. It is the default here, reaches the same quality at a smaller size and plays in current browsers. Pick VP8 only when a specific old player can't decode VP9.

Why is my WebM larger than the original MP4?

The default CRF of 23 aims for high quality, and phone MP4s are often already compressed efficiently. Raise CRF to around 31–35, pick a lower Resolution or reduce 60 fps to 30 fps. A resolution preset above the source size also inflates the file.

Will the WebM play everywhere?

VP9 with Opus plays in current Chrome, Firefox and Edge and on Android. Apple devices, smart TVs and some editing programs handle WebM less reliably, so test the file where it will be used. For the widest support, keep an MP4 version made with Video to MP4.

Can I convert to WebM without losing quality?

Only if the source already contains VP8, VP9 or AV1 video: choose copy for Video codec, keep Resolution at Original and leave FPS and Video bitrate empty, and the stream is repackaged unchanged. Set Audio codec to copy as well; AAC or MP3 audio is still re-encoded to Opus. Most MP4, MOV and AVI files contain H.264 or H.265 video and are therefore re-encoded; as a rule of thumb, a CRF of 15–20 keeps visible losses small at the cost of size.

Why did my conversion fail or time out?

Each job can run for 15 minutes, and AV1 is the codec most likely to hit that limit on long 1080p or 4K clips: switch to vp9, lower the Resolution, or shorten the clip with Cut Video first.