FLV to MP4 Converter

FLV (Flash Video) was the format of early YouTube, web players and screen recorders; since Flash was retired, few players open it. Converting to MP4 makes those clips play on phones, TVs and in any editor. FLV files from the late 2000s onward usually hold H.264 video and AAC sound, which this converter moves into an MP4 unchanged — instant and lossless. Older files with Sorenson Spark (H.263), On2 VP6, MP3, Nellymoser or Speex sound are re-encoded to H.264 and AAC. It runs in your browser with the ffmpeg engine (about 30 MB, downloaded once).

How to use this tool

1. Choose one or more .flv (or .f4v) files.
2. Keep "Fastest" to copy H.264 video unchanged, or choose "Always re-encode".
3. Pick the quality for re-encoding.
4. Download the MP4 files (several come as one ZIP).

Formula

H.264 + AAC/MP3: repackaged (copied); anything else: H.264 (x264, CRF) + AAC

FLV stores each frame's display time, so copied H.264 frames keep their correct order and timing in the MP4. Sorenson Spark and VP6 cannot go into a standard MP4 and are re-encoded; Nellymoser, Speex and ADPCM sound is converted to AAC. If the MP4 container refuses a stream during copying, the file is re-encoded automatically.

Example

A 4-minute 480p H.264/AAC FLV of 25 MB is repackaged into a 25 MB MP4 in a few seconds. The same clip in Sorenson Spark must be re-encoded: at about 27 frames per second for 480p on a recent computer, 4 minutes at 25 fps takes roughly 4 minutes.