Convert FLV to FLAC — Free Online Tool
Extract and convert audio from FLV Flash Video files into FLAC, a lossless audio format that preserves every detail of the original sound. Unlike MP3 or AAC conversions, FLAC retains full audio fidelity — ideal when you want the best possible audio from an FLV source without any additional compression artifacts.
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FFmpeg Command
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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:
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DownloadHow It Works
FLV files typically carry audio encoded in either AAC or MP3 (via libmp3lame). During this conversion, FFmpeg demuxes the FLV container to extract the audio stream, then re-encodes it into FLAC using lossless compression. Because FLV audio is already lossy (AAC or MP3), the output FLAC file will be a lossless representation of that lossy audio — meaning no further quality is lost in this conversion step, but the original lossy compression artifacts from the FLV source are preserved. The video stream is discarded entirely, since FLAC is a pure audio format.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles the demuxing of the FLV container, decoding of the AAC or MP3 audio stream, and re-encoding into FLAC format. |
-i input.flv
|
Specifies the input FLV file. FFmpeg reads and demuxes this Flash Video container to access its audio stream, ignoring any video streams since FLAC is an audio-only output format. |
-c:a flac
|
Sets the audio codec to FLAC (Free Lossless Audio Codec). FFmpeg decodes the FLV's lossy audio (AAC or MP3) to PCM and then re-encodes it losslessly into FLAC, ensuring no further quality degradation occurs during this conversion step. |
-compression_level 5
|
Sets FLAC's compression effort to level 5 out of 8. This affects only encoding speed and file size — not audio quality — since all FLAC compression levels are mathematically lossless and produce bit-identical audio output. Level 5 is the widely-used default that balances compression ratio against encoding time. |
output.flac
|
Defines the output filename with the .flac extension. FFmpeg uses this extension to confirm the FLAC container format, and the resulting file contains only the losslessly compressed audio stream extracted from the original FLV. |
Common Use Cases
- Archiving audio from old Flash-era video tutorials or lectures where you want the cleanest possible audio copy for long-term storage
- Extracting a music performance or concert recording from an FLV file downloaded from a legacy video platform, preserving it in a lossless format for your audio library
- Pulling the audio from an FLV screen recording of a software demo to use as a voiceover track in a video editor, without introducing additional lossy re-encoding
- Converting FLV podcast episodes or interviews that were originally hosted via Flash players into FLAC for archival or re-editing purposes
- Extracting audio from FLV files to feed into audio mastering or analysis tools that require or prefer lossless input formats
- Recovering audio from FLV files for use in a Digital Audio Workstation (DAW), where FLAC is widely supported and preferred over lossy formats for editing
Frequently Asked Questions
The FLAC file itself is losslessly encoded — no additional quality is lost during the FLV-to-FLAC conversion. However, FLAC can only preserve what was already in the source. Since FLV audio is typically AAC or MP3 (both lossy formats), any compression artifacts introduced when the FLV was originally created will still be present in the FLAC output. Think of it as a lossless snapshot of a lossy source — perfect for archiving without further degradation.
FLV files use lossy audio codecs (AAC or MP3) that achieve small file sizes by discarding audio data the human ear is less sensitive to. FLAC instead uses lossless compression, which must preserve every audio sample exactly. Even though FLAC compresses efficiently, its files are inherently larger than their lossy equivalents. The video stream also contributed to the FLV's data, so you're comparing a full video container against a pure audio file — the size difference reflects the fundamental difference in how lossless versus lossy compression works.
The -compression_level flag in FLAC controls the trade-off between encoding speed and output file size, with values ranging from 0 (fastest, largest file) to 8 (slowest, smallest file). Critically, all compression levels produce bit-for-bit identical audio — this is not a quality setting like CRF in video encoding. Level 5 is the standard default that balances speed and file size well for most use cases. You might increase it to 8 if minimizing storage is a priority and you have time to wait, or drop it to 0 for the fastest possible encoding with negligible file size difference.
FLV containers have limited and inconsistently implemented metadata support, so useful tags are rarely present in FLV files. FLAC, by contrast, supports rich Vorbis comment metadata tags. FFmpeg will attempt to map any metadata it finds in the FLV to the FLAC output, but in practice you will likely need to add or edit tags manually after conversion using a tool like MusicBrainz Picard or a FLAC tag editor.
Replace the '5' in '-compression_level 5' with any integer from 0 to 8. For example, 'ffmpeg -i input.flv -c:a flac -compression_level 8 output.flac' will produce the most compressed FLAC file at the cost of slower encoding. For batch processing multiple FLV files on the command line, you can use a shell loop such as: 'for f in *.flv; do ffmpeg -i "$f" -c:a flac -compression_level 5 "${f%.flv}.flac"; done' on Linux/macOS, which processes every FLV in the current directory.
Yes — FFmpeg's -ss and -to (or -t) flags let you trim the output. For example, 'ffmpeg -i input.flv -ss 00:01:30 -to 00:04:00 -c:a flac -compression_level 5 output.flac' extracts only the audio between 1 minute 30 seconds and 4 minutes. This is especially useful when an FLV contains a long recording and you only need a specific segment archived as FLAC.
Technical Notes
FLV (Flash Video) is a container format that most commonly encodes audio as AAC (Advanced Audio Coding) at bitrates between 64k and 192k, or occasionally as MP3 via the libmp3lame encoder. When converting to FLAC, FFmpeg fully decodes this lossy audio stream to PCM and then re-encodes it using the FLAC lossless codec — meaning the intermediate PCM representation is complete and exact, but bounded by the fidelity of the original lossy decode. FLAC supports sample rates up to 655,350 Hz and bit depths up to 32 bits, far exceeding typical FLV audio specs (usually 44.1 kHz / 16-bit). The output FLAC file will match the sample rate and channel count of the FLV source audio. One known limitation is that FLV does not support multiple audio tracks or embedded subtitles, so there is no risk of stream mapping complexity — the single audio stream is straightforwardly extracted. FLAC's cue sheet and ReplayGain features are not populated by this conversion and would need to be added separately with dedicated tools.