Convert MKV to FLAC Online
Extract audio from MKV files to lossless FLAC. Perfect for preserving anime, movie, and series soundtracks at maximum quality. Free, in your browser.
.mkv · up to 100 MB
What you can do
MKV to FLAC: anime and cinema soundtrack at maximum quality
Stream copy for native FLAC
If the MKV already has FLAC audio, extraction is instant with zero re-encoding.
DTS-HD to archival FLAC
Decodes DTS-HD Master Audio to PCM and preserves it in FLAC with no additional loss.
100% private
Your MKV never leaves your device. FFmpeg.wasm processes everything locally in the browser.
Anime and Blu-ray remux
Compatible with the highest-quality releases from nyaa.si and archival fansub groups.
How it works
Three steps, no hassle
Upload your MKV file
Drag or select your .mkv with DTS-HD, FLAC, AC-3, AAC, or Vorbis audio. Up to 500 MB, no signup.
Extraction to FLAC
FFmpeg.wasm analyzes the MKV audio tracks. If audio is native FLAC, it extracts via stream copy (no re-encoding). For DTS-HD, AC-3, or other codecs, it decodes and re-encodes to 24-bit FLAC.
Download your FLAC
FLAC file ready for hi-fi players, DAWs, collection ripping, or permanent archiving. Download with one click.
FAQ
Got questions?
FLAC (Free Lossless Audio Codec) is lossless compression: the decompressed audio is bit-for-bit identical to the original. MP3 and AAC discard perceptually irrelevant information through psychoacoustic coding, introducing permanent loss. If the MKV contains native FLAC audio (common in archival Blu-ray rips) or PCM (Blu-ray LPCM), converting to FLAC preserves every original sample. For already lossy audio (DTS, AC-3, AAC, Vorbis), converting to FLAC wraps the decoded audio in a lossless container, preventing additional degradation in future transcodings. FLAC is the de facto standard format for high-quality audio archiving in audiophile communities and music collections.
Yes, frequently. High-quality fansub groups and releases (especially those labeled 'BD' or 'Remux') include the original FLAC audio from the Japanese Blu-ray without re-encoding. In those cases, the tool performs a direct stream copy: it extracts the FLAC stream from the MKV container and wraps it in a .flac file with no re-encoding whatsoever. This is the fastest possible operation and adds zero loss. You can verify if your MKV has native FLAC with MediaInfo: look for 'Format: FLAC' in the audio track.
DTS-HD Master Audio is a variable-resolution lossy codec (up to 24.5 Mbps), but it is a lossy codec: it already discarded information during disc mastering. When converting DTS-HD to FLAC, FFmpeg decodes the DTS-HD to PCM (typically 24-bit/48 kHz or 96 kHz depending on the disc), and FLAC compresses that PCM losslessly. The result is identical to what the DTS-HD decoder produces as analog output. You don't recover information DTS-HD discarded, but you do preserve exactly what the codec produces, without adding further loss. For archiving Blu-ray collections, this workflow is standard.
Commercial movie MKV files (Blu-ray remux) typically have multiple tracks: the main DTS-HD MA or Dolby TrueHD track in the original language, AC-3 core or EAC-3 compatibility tracks for players without DTS-HD decoders, and in some cases audio description (AD) or additional language tracks. By default, the tool extracts the track marked as 'default' in the MKV metadata (FlagDefault=1 in the TrackEntry element). In most quality remuxes, that default track is the highest-quality one.
Yes. Hi-fi portable audio players (DAPs) from Astell&Kern, FiiO, HiBy, iBasso, and Sony Walkman NW-A/WM series all support FLAC natively, including 24-bit/192 kHz FLAC. On smartphones, iOS has supported FLAC since iOS 11 (2017) in the Music app, and Android has supported FLAC since Android 3.1 (2011). VLC, foobar2000, MusicBee, Roon, Audirvana, and virtually all desktop players decode FLAC. The only environment where FLAC has limitations is the Apple ecosystem: iTunes and Apple Music do not import FLAC directly (they accept ALAC, Apple's equivalent), though they can play it via Quick Look.
Size depends on the source codec. If the MKV has native FLAC, the resulting .flac is practically the same size as the audio stream inside the MKV (FLAC compresses PCM to approximately 50–60% of its size, typically 15–35 MB for a 24-minute episode at 24-bit/48 kHz). If the MKV has DTS-HD MA, the FLAC resulting from decoding to PCM and re-compressing with FLAC may be somewhat larger than the original DTS-HD because FLAC compresses less aggressively than DTS-HD. For a 2-hour movie with 7.1 audio at 24-bit/48 kHz, the FLAC can occupy between 600 MB and 2 GB depending on the spectral density of the soundtrack.
Convert MKV to FLAC: extract lossless audio from Matroska for archiving and hi-fi playback
Converting MKV to FLAC is the reference operation for those who prioritize preserving maximum audio quality extracted from Matroska files: anime Blu-ray collectors, film archivists, music producers, and audiophile users who maintain libraries on hi-fi players including DAPs, DAC amplifiers, and Roon. The Matroska container stores audio in tracks with specific CodecID values: A_FLAC for native FLAC which is the most technically advantageous case, A_DTS for DTS and DTS-HD Master Audio, A_TRUEHD for Dolby TrueHD with Atmos support, A_AC3 for Dolby Digital and EAC-3, and A_AAC for Advanced Audio Coding. The highest-quality releases in communities like nyaa.si labeled FLAC or Remux contain the original FLAC stream from the Japanese Blu-ray without re-encoding, frequently at 16-bit/48 kHz or 24-bit/48 kHz depending on the original disc mastering. FLAC, released by Josh Coalson under BSD license in July 2001, implements the linear prediction algorithm (LPC) with up to 32 prediction coefficients and Rice coding for residuals, achieving typical compression ratios of 50 to 65 percent for musical audio under normal conditions. Unlike lossy codecs such as MP3, AAC, Vorbis, and Opus, FLAC guarantees without exception that the decompressed audio waveform is bit-for-bit identical to the original, which is absolutely critical both for long-term permanent archiving and for music production pipelines where each additional transcode accumulates irreversible and irrecoverable loss of spectral and temporal audio information. This mathematical guarantee of identity makes FLAC the unambiguous standard for anyone building a serious long-term audio archive from high-quality Matroska source material, whether that material originates from commercial Blu-ray discs, independent film productions, or archival recordings captured in Matroska format.
The most frequent workflows for MKV to FLAC conversion are four. First, native FLAC audio extraction from anime releases: the most technically efficient case, where the FLAC stream is extracted by direct copy from the MKV container without any re-encoding, preserving exactly the original bits from the Japanese Blu-ray exactly as mastered by the studio. Tools like mkvextract from MKVToolNix perform this operation identically but require local installation on the operating system; this tool runs it directly in the web browser with no additional software needed. Second, DTS-HD Master Audio to FLAC conversion for Blu-ray collection archiving: FFmpeg's DTS-HD decoder decodes the signal to high-resolution PCM at 24-bit/48 kHz or 24-bit/96 kHz depending on the disc, and the FLAC encoder compresses that PCM completely losslessly, which is the established standard in digital film preservation communities worldwide. Third, audio extraction for speech recognition preprocessing: FLAC is the preferred input format for APIs like OpenAI Whisper, Google Speech-to-Text, and Azure Cognitive Services because it allows verifying via the STREAMINFO MD5 hash that the delivered audio is identical to what was captured, without compression artifacts that degrade recognition accuracy in the model. Fourth, material preparation for mastering and mixing: post-production studios receiving production MKV files extract audio to FLAC before importing to Pro Tools, Logic Pro, or Adobe Audition to guarantee they work with the original signal without accumulated lossy generations. Each of these four workflows benefits specifically from FLAC's combination of lossless fidelity, broad software support across all major DAWs and media players, and the built-in integrity verification via STREAMINFO MD5 that allows archivists to confirm file authenticity years after the original conversion was performed.
Convertir.ai runs MKV to FLAC conversion entirely in the browser using FFmpeg.wasm compiled with support for all relevant decoders including DTS-HD, TrueHD, and native FLAC. The flow begins with analysis of the MKV file's EBML header to determine the DocType (matroska or webm) and the Matroska schema version in use. The Segment's SeekHead provides absolute offsets for the Tracks, Info, and Cues blocks, allowing direct access to track descriptions without linearly reading the entire file, which matters for large Blu-ray remux MKV files that can exceed 20 GB in size. The default audio track is identified by TrackType=2 and FlagDefault=1 in TrackEntry elements within the Tracks block. When the CodecID is A_FLAC, FFmpeg performs complete stream copy: reads the FLAC data blocks from the MKV, strips the Matroska encapsulation header wrapping them, and writes them directly to the output FLAC container including the STREAMINFO block with sample rate, bit depth, number of channels, total sample count, and MD5 hash of decoded audio for future integrity verification. When the CodecID is A_DTS or A_TRUEHD, FFmpeg uses the corresponding decoder to produce 32-bit float PCM, which the FLAC encoder converts to 16 or 24-bit integers based on the track's native resolution and compresses at compression level 5, the optimal balance between encoding speed in the WebAssembly environment and the resulting compression ratio. MKV metadata including title, artist, creation date, and duration is transferred to the VORBIS_COMMENT blocks of the output FLAC for compatibility with foobar2000, MusicBee, and Roon. The entire conversion runs client-side in WebAssembly with no server uploads, ensuring complete privacy for personal Blu-ray collections and archival recordings regardless of their sensitivity or commercial content.