Multi-Track Audio — Audio Description (MKV)
A main audio track plus an audio-description track for blind and low-vision viewers, carrying the `visual_impaired` disposition. The description track is an octave and a bit below the main track, so selecting it is audible. Matroska has exactly one flag for this — there is no separate `descriptions` flag as there is in MP4 and in HTML's own track kinds — so a converter that maps `kind="descriptions"` onto Matroska has to pick this one, and a converter going the other way has to infer it. Both tracks are tagged `eng`, which is the realistic case and the awkward one: a picker that lists tracks by language shows two identical entries, and only the flags tell them apart. Broadcast and streaming compliance regimes increasingly require this track to be present and correctly flagged, and the flags are exactly what a naive `ffmpeg -c copy` remux drops.
Rendered preview of the mkv file (156.3 KB). Download above for the original.
Specifications
- Audio Tracks
- 2
- Track0
- eng, 440 Hz, main programme, default flag
- Track1
- eng, 196 Hz, visual_impaired flag
- Flag Note
- Matroska has no separate 'descriptions' flag — visual_impaired is the one
- Codec
- AAC LC 64 kbps 48 kHz
- Duration
- 8s
What is a .mkv file?
MKV (Matroska) is a flexible open multimedia container that can hold virtually unlimited video, audio, subtitle, and attachment tracks with rich metadata and chapters. It is codec-agnostic and popular for high-quality video with multiple audio and subtitle options. It is a superset of the design behind WebM.
How to use this file
Use an example MKV to test multi-track demuxing, subtitle and chapter extraction, codec detection, and remuxing or transcoding pipelines.
How to use this file for testing
“Multi-Track Audio — Audio Description (MKV)” is a deterministic Novus Examples fixture for Media accessibility, Video QA, Video codecs, Conversion testing. Containers carrying several subtitle and audio tracks at once, with real language tags and the default, forced, hearing-impaired and visual-impaired flags actually set — for testing track pickers, accessibility menus, and the flag handling that only shows up when more than one track exists.
Documented properties for this file: 8s. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.
Media fixtures are short and synthetic by design. Prefer waveform or transcript ground truth in the same group when measuring ASR, trim, upscale, or sync tools; do not assume broadcast-quality masters.
Code examples
<video controls preload="metadata" width="640" src="mkv-audio-description.mkv"></video>Related files
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Generated by generation/video_accessibility.py. Free for any use, no attribution required — license.