Convert FLV to MP4 Online
Turn FLV files into MP4 directly in your browser using ConverterUp. There is no upload, no waiting in a queue, and no account required — your files stay on your device while WebAssembly does the work locally. Adjust quality and dimensions where supported, then download the result. The output keeps the visual fidelity you'd expect from a desktop app while running entirely in the browser tab.
Convert FLV to MP4 nowHow to convert FLV to MP4
Open the converter
Click the button to open the FLV to MP4 tool. It loads instantly — no install, no signup.
Drop your FLV file
Drag your FLV file into the upload area or click to browse. The file stays in your browser memory only.
Download MP4
The conversion runs locally and finishes in seconds. Click download to save the MP4 file to your device.
FLV vs MP4 at a glance
Key technical differences between the two formats, so you know what to expect before converting.
| Feature | FLV | MP4 |
|---|---|---|
| Type | Video container | Video container |
| Compression | Lossy | Lossy |
| Audio track | Yes | Yes |
| Common codecs | Sorenson Spark, VP6, H.264, MP3, AAC | H.264, H.265, AV1, AAC |
| Browser support | Not playable natively | All browsers |
| Extensions | .flv | .mp4 |
| MIME type | video/x-flv | video/mp4 |
| Introduced | Macromedia (now Adobe) | 2003 · MPEG (ISO/IEC 14496-14) |
What changes when you convert FLV to MP4
- FLV and MP4 are containers. The video and audio streams are re-encoded into codecs that MP4 supports (typically H.264, H.265, AV1), so you get a file that plays reliably rather than a simple rename.
- The audio track is carried over to the MP4 file, re-encoded if needed.
- Compatibility improves: MP4 opens in more browsers, apps and operating systems than FLV.
- FLV is a legacy format that browsers cannot play directly. Converting to MP4 is the easiest way to watch, share or edit old recordings.
About FLV
FLV (Flash Video) is the container used by Adobe Flash Player to stream video on the web in the 2000s. It typically holds Sorenson Spark, VP6 or H.264 video.
- Best for
- Old web video downloads and archived Flash content.
- Strengths
- Small files for its time.
- Limitations
- Flash is discontinued, so FLV files cannot be played in any modern browser.
About MP4
MP4 (MPEG-4 Part 14) is the most widely supported video container. It typically holds H.264 or H.265 video with AAC audio and plays on virtually every phone, browser, TV and editor.
- Best for
- Sharing videos, uploading to social networks and YouTube, and playback on any device.
- Strengths
- Universal playback, good compression, streaming-friendly.
- Limitations
- Lossy codecs, so repeated re-encoding gradually reduces quality.
Frequently asked questions
Is the FLV to MP4 conversion really free?
Yes. ConverterUp is fully free, with no signup, no watermarks, and no daily quota for the FLV to MP4 converter. We support the project through unobtrusive ads.
Are my FLV files uploaded to a server?
No. Conversion runs in your browser using WebAssembly. The FLV bytes never leave your device, and we have no upload endpoint at all.
What is the maximum file size?
For FLV input, the soft cap is 50 MB for images and 500 MB for video. Practical performance depends on your device's RAM.
Will the MP4 file open everywhere?
Yes. MP4 is supported by every modern browser, operating system and most apps, so it is the safe choice for sharing.
Does converting FLV to MP4 keep the sound?
Yes. The audio track is kept and, if necessary, re-encoded into a codec that MP4 supports.
Related guide
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