What happens when you convert MP3 to FLV
- FLV is a video format. The audio is encoded as AAC audio, and by default the file has no picture.
- Tick "Add a black video track" if the FLV is going to YouTube or another site that rejects audio-only video.
How to convert MP3 to FLV online
- Press "Choose MP3 files" and select one or more files, or drag them onto the box. You can add files of any size your device can hold in memory.
- Adjust the settings if you need to: resolution and quality control the size of the result. The defaults suit most people.
- Press "Convert to FLV". The first audio or video conversion downloads the converter engine, about 32 MB, which your browser then keeps for next time.
- Save each FLV with its download button. Close the tab and every trace of the files is gone from memory.
Why convert MP3 to FLV?
MP3 files usually come from music libraries, podcasts and anything that has to play everywhere. People convert them to FLV because FLV is still requested by a few legacy streaming and e-learning systems.
In short, MP3 is good at what it was made for, and FLV is the more practical choice when the file has to play, upload or edit somewhere else. MP3 plays in every browser, phone, car stereo and media player, while FLV does not play in browsers since Flash ended in 2020; plays in VLC.
How to convert MP3 to FLV on Windows, Mac, iPhone and Android
On Windows
Open this page in Chrome, Edge or Firefox, drag your MP3 files in from File Explorer, and press Convert. Each FLV is saved to your Downloads folder. If you prefer a desktop program, VLC can also convert MP3 to FLV: choose Media, then Convert / Save.
On a Mac
Safari, Chrome and Firefox all work. Drag the MP3 files from Finder onto the drop zone and the FLV files land in Downloads.
On iPhone and iPad
Open the page in Safari and tap Choose MP3 files. You can pick from Photos or from the Files app. The converted FLV appears in Files, in the Downloads folder; to put it in your photo library, open it there, tap Share and choose Save Video.
On Android
Open the page in Chrome, tap Choose MP3 files and pick them from Files or your gallery. The FLV is saved to the Download folder, where any file manager can find it. Keep the screen on while a long video converts, because Android may pause a tab in the background.
Best settings for MP3 to FLV
FLV is written as H.264 video with AAC audio. The Resolution setting is the one to reach for: 1080p keeps full HD detail, 720p is plenty for phones and laptops and roughly halves the size, and 480p suits email and old devices.
The quality levels map to the H.264 CRF scale where the target uses H.264, and to fixed high-quality settings for older codecs such as MPEG-2, MPEG-4 Part 2, WMV and Theora. Re-encoding always costs a little detail, so convert from the best copy of the MP3 you have.
MP3 vs FLV: the differences
| MP3 | FLV | |
|---|---|---|
| Full name | MPEG-1 Audio Layer III | Flash Video |
| Type | audio | video |
| Created by | the Fraunhofer Institute | Adobe (originally Macromedia) |
| First released | 1993 | 2003 |
| Compression | Lossy | Lossy |
| Usually contains | MP3 audio, typically 128 to 320 kbps | Sorenson Spark, VP6 or H.264 video with MP3 or AAC audio |
| In a browser | plays in every browser, phone, car stereo and media player | does not play in browsers since Flash ended in 2020; plays in VLC |
| Common uses | music libraries, podcasts and anything that has to play everywhere | old YouTube downloads and Flash-era video sites |
| MIME type | audio/mpeg | video/x-flv |
About MP3 and FLV files
What is an MP3 file?
MP3 is the most widely supported audio format there is, which is its whole appeal. At 320 kbps most listeners cannot tell it from the original; at 128 kbps cymbals and applause start to smear.
What is an FLV file?
FLV powered YouTube and most web video until about 2010. Since browsers dropped Flash at the end of 2020, FLV files need converting or a desktop player.
MP3 to FLV not working? Common problems
- The conversion is slow. Audio and container changes take seconds, but re-encoding video runs on your own processor. Lower the resolution to 720p, close other tabs, and keep the device plugged in.
- The tab stops or reloads on a very large file. Browsers limit how much memory one tab can use, around 2 GB and less on phones. Split long recordings or convert them on a computer.
- The FLV will not play on an old device. Try the other formats offered for MP3, or choose 720p, which older players handle more reliably.
Convert MP3 to FLV with ffmpeg
This converter runs ffmpeg inside your browser. If you would rather use the ffmpeg command line on your own computer, this command produces an equivalent FLV with the same kind of settings:
ffmpeg -i input.mp3 -c:v libx264 -crf 23 -c:a aac -ar 44100 output.flvReplace input.mp3 with the name of your file. For a whole folder of MP3 files, run the command in a loop, or drop them all on the converter above, which processes them one after another.
MP3 to FLV converter FAQ
Will I lose quality converting MP3 to FLV?
A little. Both formats are lossy, so re-encoding compounds the loss slightly. Keep the default quality or higher and the difference is rarely noticeable.
Why is the FLV a different size from the MP3?
Without a picture, the FLV is about the size of the audio. Adding a black video track adds a little, because a still black frame compresses to almost nothing.
Are my MP3 files uploaded anywhere?
No. The conversion runs inside this browser tab using ffmpeg compiled to WebAssembly, so your files stay on your device. You can disconnect from the internet after the page and converter engine have loaded and it still works.
Can I convert several MP3 files to FLV at once?
Yes. Select or drop as many files as you like; they are converted one after another and each gets its own download button.
How do I open an FLV file?
FLV does not play in browsers since Flash ended in 2020; plays in VLC. FLV is common for old YouTube downloads and Flash-era video sites.
Is this MP3 to FLV converter free?
Yes. There is no sign-up, no watermark and no limit on how many files you convert. The site is paid for by advertising, and because conversions run on your device there is no server cost per file.
Can I convert MP3 to FLV on my phone?
Yes. The converter works in Safari on iPhone and iPad and in Chrome on Android. Long HD videos convert more slowly on a phone than on a computer.