Does converting FLV to MP4 reduce quality?

Yes, slightly, because this is a re-encode to H.264. CRF 23 stays close for ordinary viewing. Old 360p Flash files are already soft, so the extra pass is less obvious than on a clean digital source. Keep the FLV if it is the only master.

Why won't YouTube or iPhone open my FLV?

YouTube has not accepted FLV uploads in years, and iPhone never shipped Flash decoders. The file can be healthy and still fail. Re-encoding to H.264 in MP4 is the practical workaround. Renaming .flv to .mp4 does not add those decoders.

Is this a remux or a re-encode?

A re-encode. Typical FLV holds VP6 or Sorenson video that MP4 players do not implement. This tool writes libx264 video and AAC audio with fast-start. Stream copy would produce an MP4 that still needs Flash-era codecs, which defeats the conversion.

Will this work on iPhone or Android?

The converter runs in Safari and Chrome. Re-encoding is heavier than a remux, so a long FLV can exhaust phone memory. Prefer a computer for anything beyond a short clip. A laptop with spare RAM is the safer host.

Can I convert several FLV files at once?

Not currently. Each encode keeps frames in memory. Convert one, download the MP4, then drop the next. After the engine loads once, later files skip that download. A folder of old lectures is still one drop each; there is no zip-of-FLVs shortcut.

Is it legal to convert FLV to MP4?

Re-encoding a capture you recorded or a file you have permission to use is the intended case. Re-encoding a commercial Flash title you do not have rights to does not become lawful as MP4. Videozify never sees the file.

FLV → MP4

FLV to MP4 Converter

Drop a file here

Click to browse, or paste a file from the clipboard.

Choose file

An FLV to MP4 converter re-encodes a Flash video file into H.264 MP4 that phones and editors open without Adobe leftovers. Drop the file, convert, and download an MP4 you can play after Flash is gone.

How to convert FLV to MP4

Drop your FLV file onto the box above, or click Browse to choose it from disk.
Confirm the selected clip is the one you want; this conversion re-encodes to H.264.
Press Convert and wait until the progress bar reaches one hundred percent.
Download the MP4 when it appears; the file saves only to this device.

Why convert FLV to MP4?

FLV is a Flash video container that YouTube, JW Player, and a thousand site embeds used before HTML5 MP4 took over. Downloads from 2006–2012, OBS-to-Flash experiments, and old screen-capture tools still land as .flv. Chrome will not play them. iPhone never did. The codec inside is often Sorenson Spark, VP6, or a later H.264-in-FLV hybrid — none of which Photos will treat as ordinary camera video.

This is not a remux page on purpose. Copying VP6 into an .mp4 name produces a file that still needs Flash-era decoders. The preset decodes the FLV and writes libx264 at CRF 23 with ultrafast, AAC at 128kbps, and fast-start so the result starts playing before it finishes downloading.

Quality of those sources is already limited: 240p, 360p, interleaved ads, capture from a browser plugin. A second H.264 pass at CRF 23 is usually less of a problem than “nobody can open this.” Keep the FLV if it is the only master from a site that no longer hosts the original.

Use this when a lecture you saved as FLV needs to go into an LMS that whitelists MP4, or when a relative emails a Flash export from an old Windows box. If you only needed the soundtrack, extract MP3 from the video instead of paying for a full re-encode.

If the MP4 is still too large for email, compress the video after converting. If you only needed one slide from a long Flash capture, trim the video instead of sending the whole hour.

FLV vs MP4: what's the difference?

	FLV	MP4
Extension	.flv	.mp4
Type	Flash video container	MPEG-4 container
Typical size (4 min)	20–60 MB	Often similar after H.264
Compression	VP6/Sorenson/H.264 + MP3/AAC	H.264 + AAC
Quality	Source Flash encode	Re-encoded (CRF 23)
Device support	Legacy Flash / VLC	Phones, web, editors

FLV is a Flash video container that old YouTube downloads and SWF-era captures used, which modern browsers will not play as a file.

Why isn't this a remux?

Because typical FLV codecs are not what MP4-on-iPhone expects. Stream-copying VP6 into an MP4 wrapper is how you get a file that still fails in QuickTime. Re-encoding writes H.264 and AAC, which is the pair those players already implement.

If your FLV already holds H.264, a remux would be smaller and lossless to the bitstream. This page still re-encodes so behaviour is predictable for the mixed pile of Flash files people actually have. Ultrafast favours finishing in a tab over the smallest possible MP4.

There is no bitrate slider for video. If the MP4 is still heavy after it plays, compress the video as a second step rather than stacking mystery settings here.

Will Chrome play an FLV if I just rename it?

No. The extension is not the codec. Flash is gone from the browser. VLC can still decode many FLV files; that does not help Mail, Drive previews, or iPhone. Re-encoding is the compatibility fix, not a rename.

Some files named .flv are actually RTMP leftovers or incomplete downloads. If conversion fails immediately, the file may be truncated. Keep the FLV and try a complete copy if you have one.

Screen recordings exported through old Adobe tools can be FLV with odd frame rates. Slight stutter in the MP4 often started in the capture, not in this encoder.

Frequently asked questions

Does converting FLV to MP4 reduce quality?: Yes, slightly, because this is a re-encode to H.264. CRF 23 stays close for ordinary viewing. Old 360p Flash files are already soft, so the extra pass is less obvious than on a clean digital source. Keep the FLV if it is the only master.
Why won't YouTube or iPhone open my FLV?: YouTube has not accepted FLV uploads in years, and iPhone never shipped Flash decoders. The file can be healthy and still fail. Re-encoding to H.264 in MP4 is the practical workaround. Renaming .flv to .mp4 does not add those decoders.
Is this a remux or a re-encode?: A re-encode. Typical FLV holds VP6 or Sorenson video that MP4 players do not implement. This tool writes libx264 video and AAC audio with fast-start. Stream copy would produce an MP4 that still needs Flash-era codecs, which defeats the conversion.
Will this work on iPhone or Android?: The converter runs in Safari and Chrome. Re-encoding is heavier than a remux, so a long FLV can exhaust phone memory. Prefer a computer for anything beyond a short clip. A laptop with spare RAM is the safer host.
Can I convert several FLV files at once?: Not currently. Each encode keeps frames in memory. Convert one, download the MP4, then drop the next. After the engine loads once, later files skip that download. A folder of old lectures is still one drop each; there is no zip-of-FLVs shortcut.
Is it legal to convert FLV to MP4?: Re-encoding a capture you recorded or a file you have permission to use is the intended case. Re-encoding a commercial Flash title you do not have rights to does not become lawful as MP4. Videozify never sees the file.