How to Convert FLV to MP4

Free desktop tools for FLV to MP4

1. 1

   Convert with FFmpeg (lossless remux option)

   Most FLV files contain H.264 video and AAC or MP3 audio — the same codecs used in MP4. You can often remux with no quality loss: `ffmpeg -i input.flv -c copy output.mp4`. If this fails or produces errors, re-encode: `ffmpeg -i input.flv -c:v libx264 -c:a aac -b:a 192k output.mp4`.

2. 2

   Convert with HandBrake

   Open HandBrake. Drop the FLV file in the queue. Set Preset to Fast 1080p30 and change the container to MP4. Under Video, choose H.264 and set RF 18–22 (lower RF = higher quality). Click Start Encode. HandBrake re-encodes the video — good for FLV files with older codecs like Sorenson Spark or VP6 that need re-encoding anyway.

3. 3

   Convert with VLC

   Open VLC. Go to Media → Convert/Save. Add the FLV file. Click Convert/Save. Set Profile to Video - H.264 + MP3 (MP4). Set an output filename with .mp4 extension. Click Start. VLC is slower than FFmpeg but requires no command-line knowledge — good for occasional conversions.

4. 4

   Verify the MP4

   Play the output MP4 in VLC or the native video player to check for sync issues or corruption. Check audio and video sync — FLV files sometimes have sync drift that gets carried over. If the sound is late or early, delay one stream against the other. This delays the audio by half a second: `ffmpeg -i input.flv -itsoffset 0.5 -i input.flv -map 0:v -map 1:a -c copy output.mp4` (adjust the offset; use a negative value to move the audio earlier).