Convert M4A to MKV — Free Online Converter

MKV (Matroska Video) is a versatile open container that supports virtually every audio and video codec. Converting M4A to MKV packages the audio inside a Matroska container, which is useful for combining audio with video tracks, adding subtitle streams, or preparing audio for media server libraries (Plex, Jellyfin, Kodi) that organize content in MKV format. The AAC audio from M4A can be stream-copied directly into MKV without re-encoding.

MKV supports multiple audio tracks, chapter markers, attachments, and metadata in ways that M4A does not. If you need to combine M4A audio with a video track, subtitles, or additional audio tracks (commentary, different languages), MKV is the standard container. Media server software like Plex indexes MKV files with their full track metadata, making MKV the preferred format for organized media libraries.

FFmpeg performs a stream copy of the AAC audio from the M4A container into an MKV container. The AAC bitstream is transferred bit-for-bit with no re-encoding. MKV (Matroska) uses EBML encoding and supports AAC natively with codec ID A_AAC. ALAC from M4A can also be muxed into MKV (codec ID A_ALAC). The operation is nearly instant since no transcoding occurs.