What is FLV and why is it no longer usable?

FLV (Flash Video) is Adobe's container format designed for the Flash Player plugin, which powered most web video from roughly 2005 to 2015. Adobe discontinued Flash Player on December 31, 2020, and all major browsers removed support. FLV files are now unplayable in Chrome, Firefox, Safari, and Edge without third-party software. Converting to MP4 is the only way to make FLV content accessible on modern devices.

What codecs does FLV use?

FLV files typically contain Sorenson Spark (H.263) or On2 VP6 video with MP3 or ADPCM audio. Some newer FLV files use H.264 video and AAC audio (these were sometimes called F4V). If your FLV contains H.264 + AAC, FFmpeg can rewrap it to MP4 with -c copy (no quality loss). If it contains Sorenson Spark or VP6, full re-encoding to H.264 is required.

Will converting FLV to MP4 reduce quality?

If the FLV contains H.264 video and AAC audio, FFmpeg can rewrap it losslessly with -c copy. For Sorenson Spark or VP6 encoded FLV files, re-encoding to H.264 introduces some quality loss. Keep the CRF value low (e.g., -crf 18) and set a bitrate at or above the source to minimize visible degradation. Since FLV source quality is often already limited, the output will generally look comparable to the original.

Why can't this tool convert the file directly in the browser?

FLV decoding and H.264 encoding require full codec libraries not available in browser APIs. The metadata reader uses the browser's built-in File API and runs entirely on your device. Actual conversion requires a desktop tool like FFmpeg, which has access to hardware acceleration (NVENC, VideoToolbox, QSV) and the full libx264/libvpx codec stack.

Is my video file uploaded anywhere?

No. The file inspector uses the browser's File API and URL.createObjectURL(). Your video file never leaves your device — there is no upload, no server processing, and no tracking of any kind.

How do I convert FLV to MP4 without losing quality?

First check if your FLV uses H.264 video by running ffprobe input.flv. If it does, use ffmpeg -i input.flv -c copy output.mp4 for a lossless rewrap. For Sorenson Spark or VP6 sources, use ffmpeg -i input.flv -c:v libx264 -crf 18 -preset slow -c:a aac -b:a 192k output.mp4. CRF 18 is near-lossless; lower CRF values produce larger files with higher quality.

Can I convert FLV to MP4 for free?

Yes. FFmpeg, HandBrake, and VLC are all completely free and open source. FFmpeg provides the most control and is ideal for batch jobs. HandBrake offers a polished GUI with presets. VLC is the simplest option if you already have it installed.

Why does my converted MP4 have no audio?

Some FLV files use ADPCM or Nellymoser audio codecs that need re-encoding. Force AAC output by adding -c:a aac -b:a 192k to your FFmpeg command: ffmpeg -i input.flv -c:v libx264 -crf 22 -c:a aac -b:a 192k output.mp4. If audio is still missing, check that your FLV actually has an audio stream: ffprobe -v quiet -show_streams input.flv.

FLV to MP4 Converter

Step-by-step guide for converting FLV video files to MP4 using FFmpeg, VLC, and HandBrake, plus a client-side FLV file metadata inspector.

Video File Inspector

Select any video file to read its metadata instantly — 100% client-side, nothing uploaded.

Click to choose a video file FLV, MP4, AVI, MOV, MKV…

FLV vs. MP4 — Format Comparison

Know what you are converting and why

Feature	FLV	MP4
Developer	Adobe (Macromedia, 2002)	MPEG group / ISO (2001)
Common codecs	Sorenson Spark, On2 VP6, H.264	H.264, H.265, AV1, AAC
Browser support	None (Flash ended 2020)	Universal — every browser
Mobile support	Not supported	Full support
Streaming	RTMP only (legacy)	HLS, DASH, progressive

FFmpeg (Recommended — full codec control)

Free, cross-platform, most flexible

FFmpeg handles all FLV variants. If your FLV already contains H.264 video and AAC audio, use -c copy for a lossless rewrap. For Sorenson Spark or VP6 sources, re-encode to H.264 with libx264.

# Install on Mac via Homebrew
brew install ffmpeg

# Install on Windows via winget
winget install ffmpeg

# Check FLV codec before converting
ffprobe -v quiet -show_streams -select_streams v:0 input.flv

# Lossless rewrap (only if FLV contains H.264 + AAC)
ffmpeg -i input.flv -c copy output.mp4

# Re-encode Sorenson Spark or VP6 FLV to H.264 MP4
ffmpeg -i input.flv -c:v libx264 -crf 22 -c:a aac -b:a 192k output.mp4

# High quality + web streaming (moov atom at start)
ffmpeg -i input.flv -c:v libx264 -crf 18 -preset slow -c:a aac -b:a 192k -movflags +faststart output.mp4

CRF 18 = near-lossless (larger file). CRF 28 = smaller file with more compression. Default CRF 22–23 is a good balance for most FLV content.

HandBrake (GUI — quality-focused encoding)

Free, Windows / Mac / Linux

Download and open HandBrake from handbrake.fr.
Drag your FLV file onto the HandBrake window to load it as the source.
In the Summary tab, set Format to MP4.
Choose a preset — Fast 1080p30 or Fast 720p30 works well for most FLV files.
In the Video tab, set the encoder to H.264 (x264) and set the RF quality slider (RF 20 is a good default; lower = higher quality).
In the Audio tab, set the encoder to AAC and bitrate to at least 128 kbps.
Click Browse to set a destination MP4 file, then click Start Encode.

VLC Media Player (GUI — no command line)

Free, Windows / Mac / Linux

Open VLC and go to Media → Convert / Save.
Click Add, select your FLV file, then click Convert / Save.
Click the Edit selected profile wrench icon next to the Profile drop-down.
In the Encapsulation tab, select MP4 / MOV.
In the Video codec tab, choose H-264 and set a bitrate (e.g., 2000 kb/s for 720p FLV).
In the Audio codec tab, choose MPEG 4 Audio (AAC) at 128 kbps or higher.
Set the destination file with an .mp4 extension and click Start.

VLC re-encodes the FLV and writes the output MP4 file to your chosen destination path.

Summary

FLV (Flash Video) is Adobe's legacy streaming container format that was dominant in the early YouTube era and Flash-based web video. Since Adobe officially ended Flash support in 2020, FLV files are no longer playable in modern browsers and are unsupported on mobile devices. MP4 (MPEG-4 Part 14) is the universal successor — supported on every browser, phone, smart TV, and streaming platform. FLV files almost always contain Sorenson Spark or On2 VP6 video with MP3 audio, which means re-encoding to H.264 and AAC is required. This guide covers three free methods — FFmpeg for maximum control, HandBrake for a polished GUI, and VLC for a no-install option — plus a browser-based metadata inspector that reads your FLV file details without uploading anything.

How it works

Click "Choose Video File" and select any FLV or video file from your computer.
The tool reads basic metadata locally in your browser — nothing is uploaded to any server.
Review the detected file name, size, duration, resolution, and MIME type.
Choose a desktop conversion method from the guides below (FFmpeg, HandBrake, or VLC).
Run the provided FFmpeg command or follow the GUI steps to produce your MP4 file.
Drop the resulting MP4 file back here to verify its metadata after conversion.

Use cases

Convert old FLV downloads from YouTube, Dailymotion, or Twitch archives to MP4.
Make FLV recordings from legacy screen-capture software playable on modern devices.
Upload FLV footage to YouTube, Vimeo, or Facebook, which no longer accept FLV input.
Play FLV files on iPhones, Android devices, or smart TVs that lack Flash support.
Preserve Flash-era web video content in a future-proof MP4 format.
Edit FLV recordings in Premiere Pro, DaVinci Resolve, or Final Cut Pro.
Batch-convert a folder of FLV files to H.264 MP4 for a media archive.
Inspect FLV metadata — codec, resolution, duration — before deciding on encoding settings.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu