MP4 to FLV Converter
Convert MP4 to FLV free — no upload, no signup
To convert MP4 to FLV, drop your MP4 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. H.264 MP4s are repackaged into FLV without re-encoding.
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 MP4 to FLV
Add your MP4 videos
Drag and drop MP4 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 FLV, Fylo repackages the file instead of re-encoding it, with no quality loss.
Convert and download
Click Convert, then download each FLV file or all of them as one ZIP.
Why convert MP4 to FLV?
FLV is still used by RTMP live-streaming tools, some legacy players and older video portals that only ingest Flash Video.
What happens when you convert MP4 to FLV?
FLV supports H.264 video and AAC audio, so a standard MP4 is copied into the FLV container without losing quality. If the MP4 uses another codec, Fylo re-encodes to H.264 and AAC at 44.1 kHz, the sample rate FLV expects.
How does Fylo convert MP4 to FLV?
Fylo reads the MP4 with ffmpeg compiled to WebAssembly and writes H.264 with AAC audio at 44.1 kHz, the sample rate Flash-era players expect. Most MP4 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 MP4 and FLV?
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.
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.
Learn more: MP4 format guide · FLV format guide
| Property | MP4 | FLV |
|---|---|---|
| Developed by | MPEG (ISO/IEC 14496-14) | Macromedia / Adobe |
| Introduced | 2001 | 2003 |
| Typical video codecs | H.264, H.265/HEVC, AV1 | H.264, Sorenson Spark, VP6 |
| Typical audio codecs | AAC, MP3 | AAC, MP3 |
| Plays in web browsers | Yes — every browser | No (Flash Player ended in 2020) |
| Compatibility | Universal: phones, TVs, editors, social media | VLC and some desktop players; RTMP live-streaming tools |
| Best for | Sharing, uploading, streaming, editing | Old Flash archives, RTMP streaming workflows |
Frequently asked questions
Can browsers play FLV?
No. Flash Player ended in December 2020, so FLV only plays in desktop apps like VLC or in streaming tools.
Will the FLV be the same size?
Yes, when the streams are copied. Re-encoded FLVs are similar in size to the MP4.
Is my MP4 file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your MP4 file is read directly from your device and never sent anywhere.
Related tools
Updated