How to use the FLV to MP4 tool
- Choose the video you want to convert.
- Leave "Fast mode" on when it appears: it changes the container without re-encoding, so it is instant and lossless. Otherwise pick a quality.
- Press Convert.
- Preview the result and download it.
About this tool
FLV (Flash Video) usually holds Sorenson, VP6, H.264 video with MP3, AAC audio and is best known for old web video and RTMP recordings. Works for FLV files that contain H.264 video with AAC or MP3 audio (most FLV files from the last decade). Older Sorenson Spark and VP6 files cannot be decoded by browsers.
MP4 with H.264 video and AAC audio is the closest thing to a universal video format. It plays on iPhones, Android phones, Windows, macOS, smart TVs and game consoles, uploads to every social platform, and previews inline in email and chat apps.
Because FLV and MP4 can hold the same codecs, this conversion is usually a rewrap: the video and audio streams are copied into a new MP4 file without being re-encoded. It takes a moment even for large files and the quality is identical. If your file uses codecs that MP4 cannot carry, the tool falls back to a normal re-encode.
Common reasons to convert FLV to MP4
- Recovering recordings saved as FLV by streaming software or old Flash-era downloads.
- Importing into editors that dropped FLV support.
- FLV files with H.264 and AAC are rewrapped into MP4 instantly with no re-encode.
FLV vs MP4 at a glance
| FLV | MP4 | |
|---|---|---|
| What it is | Flash Video | MPEG-4 Part 14 |
| Typical video codecs | Sorenson, VP6, H.264 | H.264, HEVC, AV1 |
| Typical audio codecs | MP3, AAC | AAC, MP3 |
| Best for | Old web video and RTMP recordings | Sharing, social platforms, phones, TVs and email |
| Plays on | VLC and desktop players; not phones | Practically everywhere |
Why use ToolsCrow for this
- Instant when possible. Rewrap without re-encoding.
- Private. Files never leave your device.
- No watermark. Free, no account.
- Honest errors. Unsupported codecs are explained, not hidden.
Good to know
- Works for FLV files that contain H.264 video with AAC or MP3 audio (most FLV files from the last decade). Older Sorenson Spark and VP6 files cannot be decoded by browsers.
- Output is H.264 video with AAC audio (or Opus if your browser cannot encode AAC).
Frequently asked questions
Is my video uploaded to a server?
No. Everything runs inside your browser tab using your own device's video hardware. Your file is never sent to ToolsCrow or anyone else, which also means there is no waiting for an upload and it keeps working if your connection drops after the page has loaded.
Is it really free? Is there a watermark?
It is free with no sign-up, no watermark and no daily limits. The only limits are the ones your device sets: memory and processing power.
How large a video can I use?
Because the video is processed on your device, the limit is your device's memory rather than a server quota. Phone clips of several hundred MB are fine on most devices, and desktop computers usually handle 1 to 2 GB. Files over about 4 GB are not supported.
Which browsers work best?
Current Chrome, Edge and Safari (16.4 or newer, including iPhone and iPad) work best because they include the WebCodecs video engine. Recent Firefox versions work for many files. Older browsers fall back to a much slower real-time mode or may not work at all.
Will converting FLV to MP4 reduce quality?
Not in Fast mode: the streams are copied, so quality is identical. If a re-encode is needed, the High preset keeps it visually the same and caps the bitrate so the file does not grow.
What is the difference between FLV and MP4?
FLV is Flash Video, best for old web video and RTMP recordings. MP4 is MPEG-4 Part 14, best for sharing, social platforms, phones, TVs and email.
Why does my result have Opus audio instead of AAC?
Some browsers (for example Chrome on Linux) cannot encode AAC audio. When that happens the tool saves Opus audio instead and tells you. Opus plays in Chrome, Firefox, Edge, VLC and recent Safari; if you need AAC everywhere, run the tool in Chrome or Edge on Windows or macOS, or in Safari.
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