FLV to MP4 Converter

AUTO-DELETE/Files are processed on our server and deleted as soon as conversion finishes.

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How to Convert FLV to MP4 Online

FLV to MP4: what changes in the file

This tool takes a FLV file, processes it with FFmpeg on DownloadVideo.vn servers and returns a MP4 file.

Both FLV and MP4 are lossy, so converting adds another generation of compression: a small further loss that is usually hard to notice after one conversion.

How FLV and MP4 differ

Property	FLV	MP4
Full name	Flash Video	MPEG-4 Part 14
Introduced	Macromedia/Adobe, 2003	ISO/IEC MPEG, 2003
Compression	lossy	lossy
Common codecs	Sorenson Spark, VP6, H.264, MP3, AAC	H.264, H.265/HEVC, AV1, AAC
Strengths	common in old video archives and early streaming downloads	plays on virtually every phone, browser, TV and editor; standard upload format for YouTube, TikTok, Facebook, Instagram
Limitations	Adobe Flash Player was retired in 2020 — browsers no longer play FLV; phones and modern TVs do not play it	lossy codecs: every re-encode loses a little quality

Measured with a sample file

On September 25, 2026 we ran the tool on our production server with a sample file: a 10-second 1280×720 video (FLV1 + MP3), 9.6 MB.

Result: 9.6 MB → 3.5 MB, processed in 7 s. Output: H.264 video at 1280×720, AAC audio at 44.1 kHz stereo, 128 kbps.

Real sizes depend on your content (how complex the picture and sound are, and the length); the figures only show the order of change.

Before you convert

The tool always re-encodes the picture and sound, even when the source codec would already fit the target format.
Up to 500 MB per file; a conversion that runs longer than 10 minutes is cancelled.
The file is sent to our server for conversion and deleted as soon as processing ends, including when it fails.

Frequently asked questions

Does converting FLV to MP4 reduce quality?

Slightly: it is a second round of lossy compression. One conversion is usually hard to notice, but repeated conversions add up.

How does the file size change from FLV to MP4?

With our sample file: 9.6 MB → 3.5 MB. Your file may differ depending on its content.