Web-based Media Conversion Tools

WebM (or MKV/FLV) to MP4 (fixed 1280x720 resolution) (very slow!)

The same as: ffmpeg -i input.webm -vf scale="1280:720" output.mp4

WebM to MP4 files (no transcoding, *attempts* to force high resolutions)

The same as: ffmpeg.exe -i concat:"cap.webm|input.webm" -safe 0 -c copy -avoid_negative_ts 1 -strict experimental output.mp4

WebM to Audio-only files (opus or wav)

The same as: ffmpeg -i input.webm -vn -acodec copy output.wav

MKV (or FLV/WebM) to MP4 (no transcoding)

The same as: ffmpeg -i INPUTFILE -vcodec copy -acodec copy output.mp4

Having problems?

For larger files, over 2-gigabytes in size, the browser may not be able to properly process the video in memory.
Please consider using FFmpeg [get it free here] to run these processes from the command-line instead. The corresponding commands are provided above, where you need to replace input.webm with your own file.
Other users who find FFmpeg too challenging have had luck using the graphical Handbrake application instead.