Extract Audio from FLV to MP3 — Free Online Tool
Extract the audio track from FLV (Flash Video) files and convert it to MP3 using the LAME encoder. FLV files commonly contain AAC or MP3 audio streams, and this tool re-encodes that audio to a universally compatible MP3 file — right in your browser, with no upload required.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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Settings
Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
FLV files typically carry audio encoded in either AAC or MP3 format. During this conversion, FFmpeg discards the video stream entirely using the -vn flag, then decodes the audio track — whether it was originally AAC or FLV's native MP3 — and re-encodes it using the LAME MP3 encoder (libmp3lame) at the specified bitrate. Because the output format is MP3 (not a container that could simply remux AAC), the audio is always transcoded rather than stream-copied, which takes slightly longer but produces a clean, standalone .mp3 file. The result is a widely compatible audio file stripped of all video data.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool. This is the same underlying engine running in your browser via FFmpeg.wasm (WebAssembly), so the command shown produces identical output when run locally on your desktop. |
-i input.flv
|
Specifies the input Flash Video file. FFmpeg will parse the FLV container to identify the available streams — typically a video stream (H.264 or legacy FLV codec) and an audio stream (AAC or MP3) — before processing begins. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore the video stream in the FLV file. This is essential for audio extraction — without it, FFmpeg would attempt to include video in the output, which the MP3 format cannot contain. |
-c:a libmp3lame
|
Specifies the LAME MP3 encoder for the output audio track. Since FLV audio (commonly AAC) cannot be stream-copied directly into an MP3 file, LAME decodes and re-encodes the audio into the MPEG Layer III format that all MP3-compatible devices and software expect. |
-b:a 128k
|
Sets the output audio bitrate to 128 kilobits per second, which is the widely accepted standard for general-purpose MP3 audio — balancing perceptual quality and file size. For music or high-fidelity content from the FLV source, increasing this to 192k or 320k will reduce encoding artifacts. |
output.mp3
|
Defines the output filename and tells FFmpeg to write the encoded audio as an MP3 file. The .mp3 extension also confirms the output format, ensuring ID3 tag metadata support and compatibility with the full range of MP3-aware devices and software. |
Common Use Cases
- Extracting audio from old Flash-era web video downloads (tutorials, lectures, gaming streams) saved as FLV files to listen to offline as MP3s
- Pulling the audio commentary from FLV recordings made with screen capture tools like Camtasia or Bandicam for use in podcast editing
- Converting FLV music videos downloaded from legacy platforms into MP3 tracks for playback on phones, media players, or car stereos that don't support FLV
- Archiving the audio content of FLV files before deleting the larger originals, freeing up disk space while preserving the audio
- Extracting spoken audio from FLV-format webinar recordings to generate transcripts or create audio-only training materials
- Converting a collection of old YouTube FLV downloads (from pre-MP4 era) into MP3 files compatible with modern music library software like iTunes or Plex
Frequently Asked Questions
Yes — this is a lossy-to-lossy transcode, which means some audio quality is lost regardless of the output bitrate. If the FLV file contains AAC audio, the audio is decoded from AAC and then re-encoded as MP3, introducing a second generation of compression artifacts. If the FLV file already contains MP3 audio, transcoding to MP3 again still causes minor quality degradation. To minimize loss, use the highest bitrate option (320k) if audio fidelity matters.
Stream copying (using -c:a copy) is only possible when the source audio codec matches the output format. FLV files most commonly contain AAC audio, and MP3 files cannot contain AAC streams — MP3 is both a container and a codec, and it only supports MPEG audio. Even if the FLV contains MP3 audio, FFmpeg still needs to remux it into the new container, and in practice the LAME encoder is used for reliability and metadata compatibility. Re-encoding is therefore the standard and most compatible approach.
Replace the value after -b:a in the command. For example, to encode at 320 kbps for higher quality, use: ffmpeg -i input.flv -vn -c:a libmp3lame -b:a 320k output.mp3. For smaller file sizes at acceptable quality, 128k is a common standard, while 96k or 64k are suitable for voice-only recordings like lectures or podcasts. This tool's UI lets you select the bitrate before running the conversion.
FLV files have limited native metadata support and rarely contain structured ID3 tag data. During conversion, FFmpeg will transfer any metadata it can read from the FLV container into the MP3's ID3 tags, but in practice most FLV files will produce MP3s with little or no embedded metadata like artist, title, or album. You may want to tag the resulting MP3 manually using a tool like Mp3tag after conversion.
The reduction in file size depends heavily on the video quality and length of the FLV file. Since the video stream is completely removed and only the audio is kept, a typical FLV file that is 100MB might produce an MP3 of just 5–15MB, depending on the audio bitrate chosen. Flash video files are often large due to the video component, so audio-only extraction generally yields a dramatic reduction in file size.
The single-file command shown on this page processes one file at a time, but you can run batch conversions directly in your terminal. On Linux or macOS, use: for f in *.flv; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 128k "${f%.flv}.mp3"; done. On Windows Command Prompt: for %f in (*.flv) do ffmpeg -i "%f" -vn -c:a libmp3lame -b:a 128k "%~nf.mp3". The browser-based tool on this page processes one file at a time and is best suited for individual conversions.
Technical Notes
FLV (Flash Video) is a legacy container format developed by Adobe, and most FLV files encountered today are archival downloads from the early YouTube era or recordings made with Flash-based capture tools. The two most common audio codecs found in FLV files are AAC (MPEG-4 Audio, used in most post-2008 Flash video) and MP3 (used in earlier Flash content). Both require transcoding when outputting to MP3, since MP3 is a codec-as-container format that only supports MPEG Layer III audio. The LAME encoder (libmp3lame) used here is the de facto standard for MP3 encoding and produces well-optimized output at all supported bitrates. One important limitation: FLV does not support multiple audio tracks, so there is no ambiguity about which track to extract. The -vn flag is critical — without it, FFmpeg would attempt to encode the video into the output file, which would fail since MP3 cannot contain video data. The resulting MP3 file gains broad compatibility advantages over the source FLV: it plays natively on virtually all devices, operating systems, and media players without any plugin or codec installation, which FLV notably required (Adobe Flash Player, now defunct).