Convert FLV to MP4 without re-encoding
This FLV to MP4 converter rewraps Flash Video files as MP4 so they play in any browser, on phones, TVs and editing software. Most FLV files made since 2008 — recordings from OBS Studio, saved live streams, downloads from video sites — already contain H.264 video and AAC sound, which MP4 supports directly. Those streams are copied across unchanged, so a one-hour recording converts in seconds with exactly the same picture and sound.
Older FLVs from the early Flash era use Sorenson Spark or On2 VP6 video, which no browser can decode any more. For those, the page offers FFmpeg compiled to WebAssembly: it downloads only after you press the button, then re-encodes the video as H.264. Before you convert, the page shows the codecs it found and which path it will take.
How to use the FLV to MP4 Converter
- Drop the FLV onto the box or click to choose it. The page reads the FLV header, the onMetaData block and the first tags, then shows duration, resolution, frame rate and codecs.
- Check the path label. Lossless remux means nothing is re-encoded; FFmpeg (WebAssembly) means the video uses an old Flash codec.
- If you only need the picture, set Sound → Remove sound. On a re-encode, Quality when re-encoding trades size against detail.
- Press Convert FLV to MP4 and watch the progress bar, or press Cancel to stop.
- Play the new MP4 in the preview, check its size, then press Download MP4.
FLV to MP4 Converter features
True remux
H.264, HEVC, AAC and MP3 packets are moved into the MP4 byte for byte, with each frame’s decode and presentation time taken from the FLV tags, so B-frames stay in order.
Stream and OBS recordings
Handles long recordings, timestamp gaps and the enhanced FLV format that newer streaming software uses for HEVC. Damaged or cut-off files are converted up to the last readable tag.
Old Flash codecs on request
Sorenson Spark, VP6, Screen Video, Nellymoser and Speex are converted by ffmpeg.wasm, which the page only downloads when you choose that path.
PCM sound fixed
Rare FLVs with uncompressed PCM audio get AAC sound; the video is still copied.
Nothing uploaded
Conversion happens inside this tab, so private recordings never leave your computer.
Why FLV files need converting now
FLV was the format of Adobe Flash Player, which carried most web video from YouTube’s launch in 2005 until HTML5 video took over. Adobe ended support for Flash Player on 31 December 2020 and browsers removed it, so FLV no longer plays on web pages, phones or most TVs. The format lives on as the container of RTMP live streaming, which is why stream recordings and capture software still produce it.
MP4 can hold the same H.264 and AAC streams, adds a proper index for instant seeking, and is understood by everything from iPhones to video editors. Remuxing also fixes recordings whose duration or seek bar looks wrong, because the MP4 index is rebuilt from the actual frames.
Which FLV codecs convert how
| Codec in the FLV | Typical source | What the converter does |
|---|---|---|
| H.264 + AAC | OBS, live-stream recordings, video sites after 2008 | Lossless remux in seconds |
| HEVC (H.265) + AAC | Newer streaming tools, some video sites | Lossless remux |
| H.264 + MP3 | Older downloaders and encoders | Lossless remux |
| On2 VP6 | Flash sites 2005–2010 | FFmpeg re-encodes to H.264 |
| Sorenson Spark (H.263) | Early YouTube and Flash cameras | FFmpeg re-encodes to H.264 |
| Nellymoser, Speex, ADPCM sound | Webcam and voice-chat recorders | FFmpeg converts to AAC, or remove it |
Good to know
- An MP4 with HEVC video plays on Apple devices, recent Android phones and in browsers with hardware HEVC support. If you need H.264 for older devices, re-encode the MP4 with the video converter.
- Want only the soundtrack of a stream? Extract it with Video to MP3 after converting.
- The MP4 is assembled in memory before download, so very long high-bitrate recordings need a computer with enough free RAM.
- MP4 output is written by Mediabunny (MPL-2.0); the optional converter is ffmpeg.wasm (FFmpeg, GPL-2.0-or-later), loaded unmodified into its own worker. The FLV reader is written for this page. Got other legacy files? See AVI to MP4.
FLV to MP4 Converter FAQ
How do I convert FLV to MP4 without losing quality?
Open the file in this FLV to MP4 converter. If it contains H.264 or HEVC video with AAC or MP3 sound — true for almost every modern FLV — the streams are remuxed, which means copied into the MP4 unchanged. The quality is identical and the conversion takes seconds.
Can I convert OBS or live-stream FLV recordings?
Yes. Recording software saves FLV because a crash cannot corrupt what was already written. Drop the recording here to get an MP4 for editing or uploading; the result is the same as the remux feature in the recording software.
Why does my old FLV need a 32 MB download?
FLVs from the Flash era often use VP6 or Sorenson Spark video, which browsers cannot decode. FFmpeg compiled to WebAssembly can; because it is 32 MB, the page asks before downloading it, and your browser caches it afterwards.
Is the FLV uploaded to a server?
No. The file is read and converted inside your browser tab. Only program code is fetched from a CDN, never your video.
Why is the MP4 almost the same size as the FLV?
A remux copies the same audio and video data, so only the container overhead changes — usually by less than one per cent. Use the video compressor afterwards if you need a smaller file.
Does it work with F4V files?
F4V is already MP4-based. Drop it in and the converter remuxes it to a standard MP4 in the same lossless way.