Add your MP4 file
Drop one or more .mp4 files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
MP4 to FLV
Pulling the soundtrack out of a .mp4 video into .flv audio keeps what you can hear and drops the picture entirely. Free, private, and validated — the file never leaves your browser.
Private for supported formats — processed in your browser
Runs on your deviceConvert supported files
Drop MP4 files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting MP4 video to Flash video
Pulling the soundtrack out of a .mp4 video into .flv audio keeps what you can hear and drops the picture entirely. An .mp4 file is a multimedia container that bundles compressed video, audio, subtitles, and chapter data into a single stream-friendly package. It is the default delivery format for nearly every phone, camera, and video platform, which makes .mp4 the safest target when a clip has to play everywhere.
An .flv file is a Flash Video container, the format that powered most web video during the 2000s. YouTube, news sites, and early streaming platforms delivered .flv streams into the Flash Player plugin before HTML5 video replaced the whole stack. For this route the practical draw is very small container overhead and h.264/AAC content re-wraps to MP4 without any re-encoding — balanced against no mainstream player ships FLV support anymore, which is worth knowing before you commit a large batch.
Why convert MP4 to FLV?
The usual reason to take .flv audio out of a .mp4 file is that only the sound matters — a talk, interview, song, or podcast segment. Keeping the video stream would waste storage, and a dedicated audio file is easier to trim, tag, and play. On the source side, fewer track, attachment, and chapter features than Matroska; on the target side, the payoff is very small container overhead, which is exactly what you want for recovering clips downloaded during the Flash era.
MP4 vs FLV at a glance
| Aspect | MP4 video (.mp4) | Flash video (.flv) |
|---|---|---|
| Format type | Container — quality depends on the codecs and settings inside | Container — quality depends on the codecs and settings inside |
| How it stores data | typically carries H.264/AVC or H.265/HEVC video with AAC audio, though the box structure also accepts AV1, MP3, and timed-text tracks | a simple sequence of tagged audio, video, and script packets designed for progressive download and RTMP streaming |
| Strongest at | publishing video to the web, social media, or a client who has not specified a format | recovering clips downloaded during the Flash era |
| Weak spot | fewer track, attachment, and chapter features than Matroska | no mainstream player ships FLV support anymore |
| Metadata | iTunes-style metadata atoms (title, artist, cover art) plus XMP and per-track language tags; ID3 is not native to the container | an onMetaData script tag embeds duration, dimensions, and encoder details; there is no standard field set for titles or authorship |
Pick FLV as the output
Select .flv in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if FLV is selectable, the route is real and validated.
Convert on your device
Press Convert. A WebAssembly FFmpeg build demuxes the audio track and re-encodes it locally; the video stream is simply discarded.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid FLV file. Outputs keep the original filename with the .flv extension.
MP4 to FLV questions, answered
Will converting MP4 to FLV lose quality?
Since mp4 is container-oriented and flv is container-oriented, the conversion preserves the source content exactly as stored; no additional compression pass is applied beyond what .flv itself requires.
Is it private to convert MP4 files here?
Yes — the .mp4 file is processed inside your browser tab and never uploaded. A WebAssembly FFmpeg build demuxes the audio track and re-encodes it locally; the video stream is simply discarded. Close the tab and the file is gone from memory.
Where will the FLV file work?
No current browser can play .flv, since the plugin that decoded it was removed from Chrome, Firefox, and Edge at the end of 2020. VLC and ffmpeg-based tools still read the format reliably, which is how old files get rescued into MP4.
Will the FLV file be bigger or smaller than my MP4?
Much smaller — the video stream is usually 80–95% of a .mp4 file's weight, and it is discarded entirely. The remaining audio is re-encoded at the bitrate implied by your quality setting.
What happens to the metadata in my MP4 file?
This converter strips container metadata deliberately (the FFmpeg command runs with metadata mapping disabled) so exported files do not leak recording details. In the source, iTunes-style metadata atoms (title, artist, cover art) plus XMP and per-track language tags; ID3 is not native to the container; none of it is transmitted anywhere because the file never leaves your browser.
Can I convert FLV back to MP4?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .mp4 → .flv → .mp4 is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.