Extract Audio from FLV to FLAC — Free Online Tool
Extract audio from FLV video files and save it as lossless FLAC, preserving every bit of the original audio data. Because FLV files commonly use AAC or MP3 audio internally, this tool transcodes that compressed stream into FLAC's lossless encoding — giving you the highest-fidelity archive copy possible from the source material.
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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 (Flash Video) containers typically store audio encoded in either AAC or MP3. This tool discards the video stream entirely and decodes the compressed audio stream, then re-encodes it using the FLAC codec — a lossless compression algorithm that stores the full decoded audio signal without any further quality degradation. Because the source audio in FLV is already lossy (AAC or MP3), the output FLAC file will not recover quality lost during the original FLV encoding, but it will faithfully preserve exactly what was in the FLV with no additional generation loss. The resulting FLAC file uses compression level 5 by default, which balances encoding speed and file size without affecting audio quality — all FLAC compression levels produce bit-identical audio output.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program. In the browser-based version of this tool, FFmpeg runs locally via WebAssembly (ffmpeg.wasm) with no server upload. The same command works identically in a desktop FFmpeg installation for files over 1GB. |
-i input.flv
|
Specifies the input FLV file. FFmpeg will probe the container to detect the audio codec in use (typically AAC or MP3 in FLV files) and demux the streams for processing. |
-vn
|
Disables video output entirely, stripping the FLV's video stream from the output. This is required because FLAC is an audio-only format and cannot carry video data. |
-c:a flac
|
Specifies the FLAC codec for the audio output stream. FFmpeg decodes the FLV's internal AAC or MP3 audio to raw PCM and then re-encodes it using FLAC's lossless compression algorithm. |
-compression_level 5
|
Sets FLAC's compression effort to level 5 on a 0–8 scale. This controls only encoding speed and output file size — all levels produce bit-identical audio when decoded. Level 5 is the FLAC default and offers a practical balance between processing time and compressed file size. |
output.flac
|
The destination filename for the extracted lossless audio. The .flac extension tells FFmpeg to wrap the encoded audio in a FLAC container, which supports metadata tags, cue sheets, and ReplayGain data. |
Common Use Cases
- Archive audio from old Flash-era video files (lectures, webinars, tutorials) downloaded before platforms migrated away from FLV, preserving the audio at maximum fidelity for long-term storage.
- Extract a music performance or DJ set recorded as an FLV stream capture and save it as FLAC for cataloging in a lossless music library.
- Pull the audio track from an FLV screen recording or gameplay capture to use as a voiceover or commentary clip, with no further quality loss before editing in a DAW.
- Convert FLV audio to FLAC as a lossless intermediate before subsequently transcoding to another lossy format like MP3 or Opus, avoiding double-lossy encoding chains.
- Recover audio from FLV files exported by older video editing or streaming software that defaulted to the Flash container, for use in modern media players and archival systems.
- Extract spoken-word audio from FLV interview or podcast recordings into FLAC for transcription workflows or audio restoration tools that prefer uncompressed or lossless input.
Frequently Asked Questions
No — FLAC is lossless, but it cannot recover quality that was already discarded when the audio was originally encoded into the FLV as AAC or MP3. What FLAC guarantees is that no additional quality loss is introduced during this extraction. The output FLAC is a perfect lossless snapshot of the decoded FLV audio, making it the best possible copy you can obtain from that source file.
FLV files store audio in a lossy compressed format like AAC or MP3, which achieves very small file sizes by permanently discarding audio data the encoder considers imperceptible. FLAC uses lossless compression, which must retain every sample of the decoded audio signal. Even with FLAC's compression, lossless audio files are significantly larger than lossy equivalents — typically 3 to 5 times the size of a comparable MP3 or AAC stream. This size increase is expected and reflects the fact that the full audio waveform is now preserved.
Yes, indirectly. FFmpeg must first decode whatever audio codec is inside the FLV — AAC or MP3 are both common — and then re-encode the raw decoded signal into FLAC. The decoding step is transparent, so the process works regardless of which lossy codec the FLV uses. However, any artifacts or frequency limitations introduced by the original AAC or MP3 encoding will be present in the FLAC output, since lossless encoding preserves the decoded signal exactly as-is.
Replace the value after -compression_level in the command. Valid values range from 0 (fastest encoding, largest file) to 8 (slowest encoding, smallest file). For example, use -compression_level 8 for maximum compression. Critically, this setting only affects encoding speed and file size — every compression level produces bit-identical audio output when decoded, so there is no audio quality tradeoff between levels. The default of 5 is a sensible middle ground for most use cases.
The single-file command shown on this page can be adapted for batch processing in a terminal. On Linux or macOS, use a shell loop: for f in *.flv; do ffmpeg -i "$f" -vn -c:a flac -compression_level 5 "${f%.flv}.flac"; done. On Windows Command Prompt, use: for %f in (*.flv) do ffmpeg -i "%f" -vn -c:a flac -compression_level 5 "%~nf.flac". This is especially useful for bulk-archiving collections of FLV files, particularly for files over 1GB that cannot be processed in the browser.
FFmpeg will attempt to copy any metadata embedded in the FLV container — such as title or artist tags — into the FLAC file's Vorbis comment metadata block, which is the standard tagging format for FLAC. However, FLV has limited and inconsistently implemented metadata support, so many FLV files contain little or no usable tags. If metadata is important to you, plan to review and edit the FLAC tags after conversion using a tool like MusicBrainz Picard or fre:ac.
Technical Notes
FLV is a legacy container tied to the Adobe Flash ecosystem, and its audio support is limited to AAC and MP3 — both lossy codecs. This means the FLAC output represents a lossless capture of a lossy source: the precision ceiling of the output is determined entirely by the FLV's original audio bitrate and codec quality, not by FLAC itself. The -vn flag is essential here because FLAC is a pure audio format with no video container — FFmpeg would error without it if it attempted to include the video stream. FLAC supports up to 32-bit sample depth and sample rates up to 655,350 Hz, far exceeding what FLV audio typically delivers (usually 16-bit, 44.1 kHz or 48 kHz), so the FLAC codec itself is never a limiting factor. One known edge case: some FLV files produced by older RTMP stream recorders may have audio/video sync drift or variable sample rates; FFmpeg generally handles these gracefully during decode, but if you encounter audio that sounds sped up or slowed down in the output, the source FLV likely has timestamp irregularities that may require additional flags like -af aresample=async=1 to correct.