BYTETOOLS

FLV to MP4 Converter

Convert old Flash FLV videos to MP4 online, free. Re-encodes to H.264 + AAC so clips play on any modern device — processed locally, never uploaded.

Drop an FLV file here or click to browseYour video is processed locally and never uploaded. Long videos take a while to encode.

What is the FLV to MP4 Converter?

The ByteTools FLV to MP4 Converter rescues videos from the Flash era. FLV was the web's video format for a decade, but since Flash died nothing modern plays it.

  • Plays FLVs from the Flash era on any modern device
  • H.264 video + AAC audio — the universal MP4 combination
  • Quality (CRF) control for the size/quality trade-off
  • 100% local — files are never uploaded
  • Free and unlimited, no watermark

How to use the FLV to MP4 Converter

  1. 1

    Drop an FLV file onto the box or click to browse for one.

  2. 2

    Adjust the quality (CRF) slider if you want a smaller or sharper file.

  3. 3

    Click Convert to MP4 and wait while the in-browser engine re-encodes it.

  4. 4

    Preview the MP4 and download it.

About the FLV to MP4 Converter

The ByteTools FLV to MP4 Converter rescues videos from the Flash era. FLV was the web's video format for a decade, but since Flash died nothing modern plays it. This tool re-encodes the video to H.264 and the audio to AAC inside an MP4 container — the combination every phone, browser, TV and editor understands.

It is for anyone with a folder of old downloaded clips, recordings from early streaming sites or archives from legacy screen recorders. Because many FLVs use ancient codecs (Sorenson H.263, VP6), a full re-encode is required rather than a fast remux — the tool does this with a quality slider so you control the size/quality trade-off.

Everything runs 100% locally in your browser via WebAssembly — your files are never uploaded. Re-encoding video in the browser is CPU-intensive, so long or high-resolution FLVs take time; typical short Flash-era clips convert quickly.

Frequently asked questions

How do I open an old FLV file in 2026?

The practical answer is to convert it to MP4. Flash is gone and almost nothing plays FLV natively any more. Drop the file on this tool and it re-encodes to H.264/AAC MP4, which plays everywhere from phones to smart TVs.

Why does FLV need re-encoding instead of a fast remux?

Many FLV files use obsolete codecs like Sorenson H.263 or VP6 that the MP4 container does not support, so the streams cannot simply be copied across. Re-encoding to H.264 and AAC is what makes the video universally playable.

Does converting FLV to MP4 lose quality?

There is some loss from re-encoding, but FLV-era videos are usually low resolution to begin with, and at the default quality setting the difference is rarely visible. Lower the CRF value if you want to preserve maximum detail.

Is my FLV file uploaded to a server?

No. The conversion runs entirely inside your browser using a WebAssembly build of ffmpeg. Your file never leaves your device, which also means old personal recordings stay private.

Why is the conversion slow for long videos?

Because your own computer does the encoding rather than a server farm. Short clips finish fast, but long or HD files take a while — keep the tab open and let it run.

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