FLV to MP4

How to use it

1. Choose your FLV videos, or drag them onto the box.
2. The page checks what is inside each file, then converts it on your device.
3. Download each MP4, or all of them together as a ZIP file.

Which FLV files work

Most FLV files made since about 2008 hold H.264 video with AAC sound. These are moved into the MP4 unchanged, usually in seconds, with no loss of quality. Older FLV files with Sorenson Spark video and MP3 sound are converted.

FLV files with VP6 video, common in files from about 2005 to 2008, are not converted yet while FilePresto checks their licensing position, and neither is Nellymoser or Speex sound. The page says so before anything starts.

How it works

Browsers cannot read these files on their own, so the page uses FilePresto's own converter: a small build of the open-source FFmpeg, made by FilePresto, that only reads files. It downloads once, about 0.7 MB, before your file is opened, and nothing is sent anywhere afterwards. The pictures and sound it reads are turned into H.264 video and AAC sound by your browser's own encoders, which is what makes the MP4 play everywhere. The converter's source code and build instructions are published on the licences page.

What is kept

The main video and its sound are kept. Subtitles and any extra sound tracks are left out, and the result says when this has happened. Surround sound is mixed down to stereo.

Limits

Videos are converted in the browser's memory, so very large files are refused before anything starts; the page shows the largest size tested on your kind of device. Converting older formats means decoding every picture and encoding it again, so it takes longer than simply rewrapping a file, and the page must stay open and on screen while it works, particularly on a phone.

Questions