Convert FLAC to MKV — Free Online Converter

MKV (Matroska Video) is an open-standard container that can hold virtually any audio, video, or subtitle track. Unlike most video containers, MKV natively supports FLAC audio without re-encoding — the FLAC bitstream can be copied directly into the Matroska container. This makes FLAC to MKV conversion nearly instant and completely lossless. The primary use case is packaging lossless audio alongside video tracks, subtitles, or metadata in a single Matroska file.

MKV is the preferred container for archiving high-quality video with lossless audio. Blu-ray rips, remuxes, and high-bitrate encodes frequently use FLAC audio inside MKV because it provides better compression than PCM while remaining lossless. MKV also supports multiple audio tracks, so FLAC can sit alongside a lossy AAC track for devices that do not decode FLAC. Additionally, MKV's chapter and attachment support allows embedding cover art, fonts, and navigation metadata.

FFmpeg uses stream copy (-c:a copy) to remux FLAC audio into an MKV container without re-encoding. The FLAC codec is natively supported by Matroska (codec ID A_FLAC). MKV's EBML (Extensible Binary Meta Language) structure allows arbitrary numbers of audio, video, and subtitle tracks with per-track language tags. Chapter markers use the Matroska Chapters specification. The muxing operation is near-instant since no transcoding occurs.