WebM to MP4 Converter
Convert WebM videos — screen recordings, browser downloads and web clips — to MP4 that plays on iPhones, TVs and editors, with full control over quality, bitrate, frame rate, resolution and audio.
Also: MKV to MP4 converter · AVI to MP4 converter · MOV to MP4 converter · FLV to MP4 converter · TS to MP4 converter · WMV to MP4 converter · MPEG to MP4 converter · 3GP to MP4 converter · M4V to MP4 converter · MOD to MP4 converter · VOB to MP4 converter · MTS to MP4 converter · OGV to MP4 converter · RM/RMVB to MP4 converter · MXF to MP4 converter · MP4 compressor · Video to MP3 extractor · MP4 to GIF converter · Video format converter
Click to choose a video, or drag and drop
Choose a WebM file — MKV, AVI, MOV, TS, FLV and most other formats are accepted too. Stays on your device.
Your video is converted entirely in your browser and is never uploaded. The converter engine (ffmpeg, ~32 MB) is downloaded once and cached by your browser.
Frequently asked questions
Why won’t my WebM video play on my iPhone, TV or editor?
WebM normally holds VP8 or VP9 video with Opus or Vorbis audio. Many iPhones, smart TVs, car stereos and video editors do not support those codecs. Converting to MP4 with H.264 video and AAC audio makes the video play almost everywhere.
Is converting WebM to MP4 lossless?
No. WebM and MP4 use different codecs, so the video has to be re-encoded, and any re-encode is slightly lossy. Use CRF 18 or lower for a result that looks identical, or a higher CRF for a smaller file. The file can end up larger than the original WebM, because VP9 compresses more efficiently than H.264.
Can it convert AV1 WebM files?
Only by copying. The in-browser engine can decode VP8 and VP9 but not AV1, so an AV1 video cannot be re-encoded to H.264 here. It can still be copied into an MP4 as AV1, with the audio converted to AAC, which plays on recent phones, browsers and TVs. For an H.264 copy of an AV1 file, use ffmpeg on your own computer.
Is my video uploaded anywhere?
No. The conversion runs entirely in your browser using ffmpeg compiled to WebAssembly. Your video never leaves your device. Only the converter engine itself (about 32 MB) is downloaded, once, and cached by your browser.
What is Fast remux and when should I use it?
A WebM file is just a container. If the video inside is H.264 (or another format MP4 supports) and the audio is AAC, MP3 or AC-3, those streams can be moved into an MP4 container as they are. That takes seconds and loses no quality at all. The tool checks your file and picks this automatically when it is possible.
What do CRF and bitrate mean?
CRF (constant quality) lets the encoder spend as many bits as each scene needs: lower numbers mean better quality and bigger files, around 18 looks near-lossless, 23 is the default and 28 is noticeably smaller. A target bitrate instead aims for a fixed number of kilobits per second, which gives a predictable file size but variable quality.
Why is re-encoding slow, and is there a size limit?
Re-encoding runs on a single CPU thread inside the browser (H.264 only), so it is usually near real-time speed or slower for HD. The finished MP4 also has to fit in browser memory, which in practice limits output to roughly 1 to 2 GB. For a long movie, use Fast remux, trim it, or copy the generated command and run it with ffmpeg on your own computer.
What happens to subtitles?
MP4 supports text subtitles only. SRT, ASS/SSA and WebVTT tracks are converted to the MP4 text format, and you can also save a track as a separate .srt file. Picture-based subtitles from Blu-ray or DVD (PGS, VobSub) cannot be converted.