Split MKV into Chapters Using FFmpeg

This guide demonstrates how to split a Matroska (MKV) video file into individual segment files based on its internal chapter markers using FFmpeg. You will learn the exact command-line instructions needed to automatically detect chapters and extract them either instantly without losing quality or with frame-accurate precision.

The Fast Method: Split Without Re-encoding (Lossless)

To split an MKV file quickly, you can copy the video and audio streams directly. This process takes only a few seconds because it does not re-encode the video.

Run the following command in your terminal or command prompt:

ffmpeg -i input.mkv -c copy -map 0 -f segment -segment_at_chapters 1 output_%03d.mkv

How this command works: * -i input.mkv: Specifies your source video file. * -c copy: Copies all video, audio, and subtitle streams without re-encoding, preserving original quality. * -map 0: Ensures all streams (multiple audio tracks, subtitles) from the input file are included in the split files. * -f segment: Tells FFmpeg to use the segment muxer to split the file. * -segment_at_chapters 1: Instructs FFmpeg to split the video at the exact timestamps defined by the internal chapter markers. * output_%03d.mkv: Defines the output naming convention. %03d is a placeholder that generates sequential numbers starting at 000 (e.g., output_000.mkv, output_001.mkv).

Note: Because this method copies the streams without re-encoding, FFmpeg must split the file at the nearest keyframe (I-frame) to the chapter marker. This may result in slight timing discrepancies of a fraction of a second at the start or end of a segment.

The Precise Method: Frame-Accurate Splitting (With Re-encoding)

If your splits must be frame-accurate down to the exact millisecond of the chapter marker, you must re-encode the video. This process takes longer but ensures the video cuts precisely at the chapter line.

Run this command to re-encode the segments using the x264 video encoder and AAC audio encoder:

ffmpeg -i input.mkv -c:v libx264 -crf 22 -c:a aac -map 0 -f segment -segment_at_chapters 1 output_%03d.mkv

How this command works: * -c:v libx264: Re-encodes the video stream to H.264 format. * -crf 22: Sets the Constant Rate Factor for quality (lower values mean higher quality; 18–23 is standard). * -c:a aac: Re-encodes the audio stream to AAC.