WebM to MP4 — free online tool
A WebM video recorded from a browser or downloaded from a website does not always open on your phone or in your editing software. This tool converts it to MP4, with picture and sound in codecs played almost everywhere. Your file is deleted after you download it.
Drop a WEBM file here, or click to choose one
Processed temporarily, deleted afterDrop a WEBM file here, or click to choose one
WEBM
How it works
Where your WebM files come from
WebM files come mostly from three sources: recordings made in the browser (online screen recorders, the MediaRecorder API in Chrome and Firefox), open web videos and animations embedded in websites. What they have in common is the use of VP8 or VP9 for the picture and Opus or Vorbis for the sound, codecs that many devices and programs do not recognize.
What the conversion does
Since MP4 does not hold VP9, the tool cannot just change the packaging: it decodes the video and re-encodes it with an MP4-compatible codec, generally H.264, then encodes the audio as AAC. This takes time, proportional to length and resolution, but it produces a file that plays on iPhone, Android, TVs and in the main editing programs.
Steps to follow
Choose your .webm file, start the conversion and wait for the download button. For a screen recording several hours long, first trim it with the video trimmer: you will save time and avoid processing unneeded sections. Then open the MP4 to check that it plays smoothly and that the sound is there.
Typical cases
Turning a meeting or class recording made in the browser into a file to share by email, importing a WebM clip into editing software that rejects that format, or sending a capture to someone who uses an iPhone. MP4 is also what most publishing platforms and file upload forms require.
Duration and smoothness problems
WebM recordings made in the browser sometimes have timestamp defects: a duration shown as zero, being unable to seek in the video, a variable frame rate. Re-encoding generally fixes the seek bar, because it rebuilds the file's structure. If a slight desync persists, it was already present in the original recording.
Quality and tips
Re-encoding causes a slight loss, negligible for everyday use. Avoid converting the same file several times. If the resulting MP4 is too large for your needs, follow up with the video compressor. For the reverse operation, intended for the web, use the MP4 to WebM page.
Limitations
Only .webm files are accepted. The conversion is a re-encode, so it takes longer than a remux and involves a slight loss. Defects present in the original recording, such as an audio/video offset, are not always corrected.
Frequently asked questions
Why won't my WebM open on my phone?
Because the VP8/VP9 and Opus codecs are not supported everywhere, notably on older versions of iOS. An MP4 with H.264 and AAC plays almost universally.
Is the conversion lossless?
No, it is a re-encode: the quality stays very close to the original but is not byte-for-byte identical. For everyday use, the difference is hard to notice.
Why does my WebM video show no duration?
Many recordings made in the browser do not write the duration into the file. After conversion to MP4, the index is rebuilt and the seek bar works normally.
Will the sound be kept?
Yes, the Opus or Vorbis audio is re-encoded to AAC in the MP4. If the original WebM had no audio track, the MP4 will be silent.
Can I convert a WebM to GIF?
Yes, the Video to GIF tool accepts WebM files. First cut out a short section so the GIF stays light.
How long does the conversion take?
It varies with the file's length and resolution. A few seconds is enough for a short clip, several minutes for a long high-definition video.