FLV to MP4 Converter
Convert FLV to MP4 free — no upload, no signup
To convert FLV to MP4, drop your FLV video into the box below and click Convert. Fylo converts with ffmpeg running inside your browser, so nothing is uploaded and there's no signup or watermark. Most FLVs already hold H.264, so they're repackaged in seconds.
Drop videos here
or tap to browse · paste with Ctrl+V · add many at once
Your files never leave your device
If the video already uses codecs that fit the new format, Fylo repackages it instantly with no quality loss.
Advanced
How to convert FLV to MP4
Add your FLV videos
Drag and drop FLV files into the box or tap to choose them. The converter engine (about 31 MB) downloads once, the first time you convert.
Choose quality (optional)
Balanced quality suits most videos. If the codecs already fit MP4, Fylo repackages the file instead of re-encoding it, with no quality loss.
Convert and download
Click Convert, then download each MP4 file or all of them as one ZIP.
Why convert FLV to MP4?
Flash Player is gone, so old FLV downloads and archives can't be played in browsers anymore. MP4 makes them watchable on any device.
What happens when you convert FLV to MP4?
Modern FLVs contain H.264 video and AAC or MP3 audio, which Fylo copies straight into MP4 — fast and lossless. Older FLVs using Sorenson Spark or VP6 are re-encoded to H.264.
How does Fylo convert FLV to MP4?
Fylo reads the FLV with ffmpeg compiled to WebAssembly and writes H.264 (x264, constant quality CRF 23) with AAC audio, plus the faststart flag for instant web playback. Most FLV files already contain H.264 video, so Fylo usually copies the video without re-encoding (and converts only the audio if needed), which is fast and lossless. Only the first video and audio track are kept, and the original resolution is preserved unless you pick 1080p, 720p or 480p under Advanced.
What's the difference between FLV and MP4?
FLV (Flash Video) was introduced with Flash Player 6 and 7 in 2002–2003 and became the format behind early YouTube, news sites and video portals. Later FLVs usually contain H.264 video and AAC audio — the same codecs as MP4.
MP4 (MPEG-4 Part 14) is a container format standardised in 2001 and based on Apple's QuickTime file structure. A container holds separately compressed video and audio streams plus metadata such as subtitles, chapters and cover art. Most MP4s use H.264 video and AAC audio; newer files may use H.265 (HEVC) or AV1.
Learn more: FLV format guide · MP4 format guide
| Property | FLV | MP4 |
|---|---|---|
| Developed by | Macromedia / Adobe | MPEG (ISO/IEC 14496-14) |
| Introduced | 2003 | 2001 |
| Typical video codecs | H.264, Sorenson Spark, VP6 | H.264, H.265/HEVC, AV1 |
| Typical audio codecs | AAC, MP3 | AAC, MP3 |
| Plays in web browsers | No (Flash Player ended in 2020) | Yes — every browser |
| Compatibility | VLC and some desktop players; RTMP live-streaming tools | Universal: phones, TVs, editors, social media |
| Best for | Old Flash archives, RTMP streaming workflows | Sharing, uploading, streaming, editing |
Frequently asked questions
Can I still play FLV files?
Only in desktop players like VLC. Converting to MP4 is the easiest way to keep them watchable.
Is quality lost?
Not when the streams are copied, which is the case for most FLVs from the last decade.
Is my FLV file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your FLV file is read directly from your device and never sent anywhere.
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