Convert FLAC to OPUS Online
The perfect encoding chain: lossless FLAC directly to Opus. Maximum quality guaranteed. Free, in your browser.
.flac · up to 100 MB
What it's for
FLAC to OPUS: the perfect lossless-to-lossy chain
Optimal quality guaranteed
Starting from lossless FLAC is the best possible starting point for any Opus encoding. No inherited artifacts.
Efficient streaming
Opus at 96 kbps from FLAC is transparent for most listeners. 10x smaller than FLAC, same listening experience.
Tags preserved
All Vorbis Comment metadata from the FLAC (artist, album, ReplayGain) are automatically transferred to the Opus file.
100% private
Your FLAC music library is never uploaded to any server. Complete local processing with FFmpeg.wasm.
How it works
Three steps, no hassle
Upload your FLAC file
Drag or select your .flac file. Lossless audio at any bit depth and sample rate. Up to 500 MB.
Direct encoding to Opus
FFmpeg.wasm decodes the FLAC to uncompressed PCM and encodes it directly to Opus. The encoder operates on the most faithful possible signal.
Download your OPUS file
The .opus file ready for streaming, distribution, or optimized storage. Up to 10 times smaller than the original FLAC.
FAQ
Got questions?
In lossy audio encoding, the quality of the result depends critically on the quality of the input signal: the better the input signal, the better the encoder's perceptual model can work. FLAC (Free Lossless Audio Codec) is a lossless compression format that stores audio with mathematically perfect fidelity to the original — every sample in the FLAC is identical to the corresponding sample in the original recording file. When converting FLAC→Opus, the libopus encoder receives the most faithful possible signal: the exact equivalent of the original uncompressed PCM. This contrasts with, for example, MP3→Opus, where the encoder receives a signal already degraded by MP3 artifacts. The result is that Opus generated from FLAC at any given bitrate has the highest possible quality: it is the optimal Opus. Technically, starting from FLAC or WAV of the same source file produces identical results (both are lossless representations), but FLAC allows handling larger music files without the size limitation of WAV, and is the most widespread lossless distribution format in high-quality music libraries (Bandcamp, HDtracks, Qobuz, TIDAL Masters in FLAC).
Opus at 128 kbps from FLAC is the practical transparency point for virtually any type of audio content, including high-fidelity music. In the perceptual evaluation studies published by Xiph.org in 2012 and confirmed by multiple subsequent independent studies, Opus at 128 kbps is indistinguishable from the lossless source in blind listening tests for the vast majority of participants. For comparison: AAC-LC at 128 kbps (Apple Music and iTunes format) requires 160–192 kbps to reach comparable transparency; MP3 LAME at maximum quality (V0, ~245 kbps) achieves similar transparency to Opus at 96 kbps. Opus at 96 kbps from FLAC is already transparent for most listeners across virtually all musical genres. Opus at 64 kbps from FLAC is transparent for most listeners on voice, pop, and rock content, though it may show small imperfections on highly transient percussion or in certain classical music genres with high high-frequency content.
Opus is technically superior to all lossy formats in the 32 to 256 kbps bitrate range according to all available independent perceptual evaluations. Vorbis (the Ogg Vorbis codec, also from Xiph.org) was the conceptual predecessor of the CELT branch of Opus and offers good quality, but Opus surpasses it at all bitrate ranges — Xiph.org considers Opus the successor to Vorbis and no longer recommends Vorbis for new projects. AAC-LC (the Apple format used in iTunes, Apple Music, YouTube, and most commercial streaming platforms) is competitive with Opus at high bitrates (128+ kbps) but inferior at low bitrates; Opus is significantly better than AAC at 64 kbps and below. HE-AAC v2 (AAC with Spectral Band Replication and Parametric Stereo) is competitive with Opus at very low bitrates (24–48 kbps) but inferior at medium-to-high bitrates. For independent distribution where you control the format, Opus is the technically superior choice. For distribution on streaming platforms (Spotify, Apple Music, YouTube Music), the format is determined internally by the platform regardless of what you upload.
It depends on the intended use. For personal archiving with maximum quality: 128 kbps stereo (complete practical transparency, 8–12x reduction vs typical FLAC). For music streaming in own applications: 96 kbps stereo (transparent for virtually all listeners, 10–15x reduction). For music podcasts with voice: 64 kbps stereo (very good quality, 15–20x reduction). For voice only: 32 kbps mono (excellent quality, maximum reduction). Xiph.org's practical rule is that Opus at 96 kbps is the point from which most listeners cannot distinguish from the lossless source in blind tests with representative musical material.
Yes. FLAC uses the same metadata system as OGG Vorbis: FLAC VORBIS_COMMENT blocks contain the same fields as Vorbis Comment tags in the OGG Opus container. FFmpeg automatically transfers all FLAC tags to the OGG Opus output: TITLE, ARTIST, ALBUM, DATE, TRACKNUMBER, GENRE, COMMENT, ALBUMARTIST, DISCNUMBER, etc. ReplayGain values (REPLAYGAIN_TRACK_GAIN, REPLAYGAIN_TRACK_PEAK, REPLAYGAIN_ALBUM_GAIN, REPLAYGAIN_ALBUM_PEAK) are also transferred, allowing players that support ReplayGain to apply the correct volume normalization when playing the Opus file.
Yes, officially. Xiph.org, the creators of both formats, explicitly recommend using Opus instead of Vorbis for all new projects since the publication of RFC 6716 in September 2012. The reasons are clear: Opus outperforms Vorbis at all bitrate ranges, has lower latency (important for streaming and interactive applications), supports lower bitrates for voice, and is under active development while Vorbis is in maintenance mode. Opus support in players and platforms has reached a critical mass since 2014–2015 that makes its adoption practical. The only scenarios where keeping Vorbis may be reasonable are compatibility with very old hardware or software that supports Vorbis but not Opus (car players with firmware from before 2015, some older DAB+ radio receivers).
Convert FLAC to OPUS: the perfect lossless-to-lossy chain for high-quality music
FLAC (Free Lossless Audio Codec) was developed by Josh Coalson and released in July 2001 as the first open-source lossless audio compression codec with mass adoption. Unlike MP3, AAC, or Opus, FLAC discards no component of the audio signal: it uses linear prediction and Rice-Golomb entropy coding to reduce file size by 40% to 60% compared to the equivalent WAV, but decoding is bit-perfect, meaning every sample of the decoded FLAC file is mathematically identical to the corresponding sample in the original uncompressed audio. This behavior makes FLAC the digital equivalent of a photographic negative: it preserves all original information and allows exact regeneration of the original signal. FLAC is the standard high-fidelity music distribution format on platforms like Bandcamp (offered as the maximum quality download option), HDtracks, Qobuz, and TIDAL in their HiFi and Masters plans. Personal audiophile libraries often accumulate collections of hundreds or thousands of albums in FLAC representing tens of gigabytes or several terabytes of storage. Converting these collections to Opus allows reducing the size by a factor of 8 to 15 while maintaining quality perceptually indistinguishable from the original FLAC according to the Xiph.org perceptual evaluation studies of 2012 and the confirming independent studies published subsequently. A 45-minute CD-quality album in FLAC takes 250-300 MB; the same album in Opus at 128 kbps takes approximately 45 MB with no audible quality difference in double-blind tests with trained listeners. All conversion occurs locally in the user's browser via FFmpeg.wasm, ensuring complete privacy. There is no limit on the number of files per session and no usage restrictions on any available function.
The technical comparison between Opus and its competitors in the lossy audio encoding market reveals clear Opus superiority in the bitrate range relevant for high-quality music distribution. The perceptual evaluation studies published by Xiph.org in 2012 used the MUSHRA protocol (MUltiple Stimuli with Hidden Reference and Anchor, defined in ITU-R BS.1534) with a panel of trained listeners and test material representative of multiple musical genres including classical, jazz, pop, and electronic. Results showed that Opus at 96 kbps obtained MUSHRA scores equivalent to AAC-LC at 128 kbps and MP3 LAME VBR V0 at approximately 245 kbps average bitrate, confirming that Opus achieves the same perceived quality at less than half the MP3 bitrate. Vorbis (the Ogg Vorbis codec, also from Xiph.org) was the conceptual predecessor of the CELT branch of Opus; Xiph.org considers Opus the successor to Vorbis and no longer recommends Vorbis for new projects. AAC-LC (the Apple format used in iTunes, Apple Music, YouTube, and most commercial streaming platforms) is competitive with Opus at high bitrates of 128 kbps or more, but inferior at low bitrates: Opus is significantly better than AAC at 64 kbps and below. In 2025 Opus remains the de facto standard for applications requiring efficient high-quality audio encoding, and the FLAC to Opus chain is recommended by the ArchLinux wiki and MusicBrainz Picard documentation for creating distribution copies of FLAC collections. The tool is compatible with Chrome, Edge, Firefox, and Safari on desktop and mobile without any additional configuration. The resulting file follows IETF and Xiph.org open standards for maximum compatibility with audio players and software.
Convertir.ai performs the FLAC to Opus conversion entirely in the browser with FFmpeg.wasm. The process decodes the FLAC using the libflac decoder, which reconstructs the bit-for-bit identical PCM to the original regardless of the FLAC's bit depth of 16, 24, or 32-bit integer, applies if necessary a resample to 48 kHz using FFmpeg's Kaiser windowed sinc filter for maximum resampling quality, and encodes with libopus at the user-selected bitrate. The Vorbis Comment metadata from the FLAC VORBIS_COMMENT block are transferred entirely to the output OGG Opus container, including ReplayGain values (REPLAYGAIN_TRACK_GAIN, REPLAYGAIN_TRACK_PEAK, REPLAYGAIN_ALBUM_GAIN, REPLAYGAIN_ALBUM_PEAK) if present in the source FLAC, allowing players that support ReplayGain to apply the correct volume normalization when playing the Opus file. The output container is OGG with .opus extension, the standard format for Opus distribution outside of WebM containers. For FLAC music collections at 24-bit/96 kHz from Hi-Res platforms like Qobuz and HDtracks, the resample from 96 kHz to 48 kHz is transparent to the human ear and does not perceptibly affect the quality of the resulting Opus at the target bitrate of 128 kbps or above. For 16-bit/44.1 kHz FLAC in CD quality, the Kaiser windowed sinc resample from 44.1 to 48 kHz is practically undetectable in blind tests. No quantity limit, no signup, no watermark, with complete privacy for personal music libraries processed locally in the browser. The process is completely free and requires no signup or installation of additional software. All conversion occurs locally in the user's browser via FFmpeg.wasm, ensuring complete privacy.