Convert FLV to MP4

Convert FLV to MP4 online. Old Flash Video files from the web and stream recorders become H.264 MP4 that every modern player opens. No upload.

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Why convert FLV to MP4?

MP4 is the most widely supported video format. Converting from FLV fixes "unsupported file" errors on phones, social sites, presentation apps and video editors.

How the conversion works

The FLV video is decoded and re-encoded to H.264 with AAC audio. That combination plays on nearly every phone, browser, TV and editor.

What is an FLV file?

FLV is Flash Video, the format behind YouTube and most web video until the early 2010s. Adobe ended Flash Player in 2020, so browsers and most players no longer open .flv files. They still turn up in old downloads, archived websites and recordings from some streaming and capture software.

How to convert FLV to MP4

Drop the .flv files above and press Convert all. FFmpeg, compiled to WebAssembly, reads the Flash container in your browser. Old Sorenson Spark and VP6 video and newer H.264 video are all re-encoded to H.264 at CRF 23, and MP3 or AAC audio becomes AAC at 160 kbps. The result is a standard MP4 with fast start. The first conversion downloads the engine.

Quality of old FLV files

Many FLV files were made for slow connections, at 320 × 240 or 480 × 360 pixels and low bitrates. Converting keeps that resolution and can't add detail. The MP4 will look like the FLV did, and it will now play on phones, TVs and in video editors.

Encoding happens on your device

Video encoding runs in this browser tab, on your own device. There is no upload and no queue. Your device does all the work, so a large or long clip can take a minute or more.

Before you start

Input: FLV. Output: MP4. The settings appear before anything runs, so you can check them first. Your original file is never changed.

Video work uses a lot of memory and CPU. Try a short clip first and check that the sound and playback work. On a phone, split large batches into smaller ones.

Keep the original until you have opened and checked the result. The work happens in this browser tab, so the size you can handle depends on your device's memory, your browser and the file itself.