Guide
FLV to MP4: old Flash videos, playable again
Drop an FLV file above and get an MP4 that plays on any phone, browser or app. The file stays on your device.
In short
- This converter turns an FLV file into an MP4 that plays on any phone or browser.
- Newer FLV files hold H.264 video, which is copied across in seconds.
- Older FLV files hold Sorenson Spark or VP6 video, which is re-encoded once.
- Nothing is uploaded. Everything runs inside this browser tab.
FLV to MP4
Runs in your browser · files never leave this page
Drop a FLV file here
or
The engine reads the file first. An H.264 picture with AAC sound is copied into the MP4 with no re-encode. Anything else is written as H.264 + AAC.
Your file never leaves this page. The engine downloads once, the work happens in this tab, and there is no upload, no account and no storage. Close the tab and the file is gone unless you downloaded it.
More free tools: Video compressor · Video resizer · Video to MP4 · Video to MP3 · Video clipper · all tools
What is an FLV file?
FLV is Flash Video, the format web video players used before Flash was retired.
- FLV files come from old web downloads, early stream recordings and archives.
- Inside an FLV you find H.264, Sorenson Spark or VP6 video, with AAC or MP3 sound.
- Adobe ended Flash at the end of 2020, and most apps no longer open FLV.
What the converter does
It copies what an MP4 can hold as it is, and re-encodes only what it cannot.
- Copied: H.264 video and AAC sound go into the MP4 untouched. No quality loss.
- Re-encoded: any other video becomes H.264 at a high quality setting (CRF 23).
- Sound: any other sound becomes AAC at 160 kbps.
- Web ready: the MP4 is set up to start playing before it fully loads.
What happens to each part of your FLV file
The first video track and the first sound track are used. The rest is left out.
| Inside the file | What you get in the MP4 | How long |
|---|---|---|
| H.264 video | Copied as is, no quality loss | Seconds |
| Sorenson Spark or VP6 video | Re-encoded once to H.264 | Minutes for a long file |
| AAC sound | Copied as is | Seconds |
| MP3 sound | Converted to AAC at 160 kbps | Seconds |
Inside the file: H.264 video
- What you get in the MP4
- Copied as is, no quality loss
- How long
- Seconds
Inside the file: Sorenson Spark or VP6 video
- What you get in the MP4
- Re-encoded once to H.264
- How long
- Minutes for a long file
Inside the file: AAC sound
- What you get in the MP4
- Copied as is
- How long
- Seconds
Inside the file: MP3 sound
- What you get in the MP4
- Converted to AAC at 160 kbps
- How long
- Seconds
This is the whole editor
Highlight a phrase and a clip lands on those exact words. No timeline, no keyframes, no layers.
How to convert FLV to MP4
Four steps, all in this tab.
FLV to MP4 in four steps
Drop your FLV file
In the box at the top
The engine reads it
Which video and sound it holds
Copy or re-encode
Only what MP4 cannot hold is redone
Download the MP4
Saved to your device
Limits of a browser tool
Everything runs on your own device, so your device sets the limits.
- File size: up to 500 MB runs comfortably. Bigger files may run out of memory.
- Speed: the engine uses one processor core, so a long re-encode takes minutes.
- First run: the engine downloads once, about 32 MB. After that it starts fast.
- Phones: it works, but a laptop is faster and has more memory.
Questions people ask
- Is FLV to MP4 fast?
- Often, yes. Newer FLV files hold H.264 video, which is copied into the MP4 in seconds. Older ones use Sorenson Spark or VP6 and are re-encoded, which takes longer.
- Does converting FLV lose quality?
- Not when the video is H.264: it is copied bit for bit. Older FLV video is re-encoded once at a high quality setting, which looks like the source.
- Why won't my FLV play anymore?
- FLV was made for the Flash player, which Adobe ended in 2020. Browsers and phones dropped it. An MP4 of the same video plays everywhere.
- Can I convert several FLV files at once?
- One at a time. Each file runs in this tab and downloads as its own MP4.
- Is my FLV file uploaded anywhere?
- No. The tool runs inside this browser tab, so your FLV file never leaves your device. Only the engine itself is downloaded, about 32 MB, once per visit.
Want a finished video with captions, not just a converted file? Cutroom edits your clip for you. Your first video is free.