Multi-Track Audio — Dual Language (MKV)
Two audio tracks with distinct language tags, and English flagged as the default. The two tracks are different pitches — 440 Hz and 659 Hz, a perfect fifth apart — so which track a player selected is audible immediately rather than something you have to inspect the file to determine. That is the whole design. Dual-language fixtures that carry the same tone on both tracks cannot distinguish 'switched correctly' from 'ignored the switch', which is the one thing you want to test.
Rendered preview of the mkv file (156.3 KB). Download above for the original.
Specifications
- Audio Tracks
- 2
- Track0
- eng, 440 Hz, stereo, default flag
- Track1
- spa, 659 Hz, stereo
- Codec
- AAC LC 64 kbps 48 kHz
- Duration
- 8s
- Resolution
- 480x270
Testing contract
Expected to pass- Scenario
- Open the file, enumerate its audio tracks, and identify each by its tone frequency.
- Expected result
- 2 AAC LC tracks at 64 kbps 48 kHz over 8s of 480x270 video: track 0 is eng at 440 Hz with the default flag, track 1 is spa at 659 Hz. The tones are the assertion - measuring the decoded frequency proves which track was actually selected, which a language tag alone cannot.
What is a .mkv file?
MKV (Matroska) is an open, codec-agnostic multimedia container that holds unlimited video, audio, subtitle, chapter, and attachment tracks in one file. Its structure is EBML, a binary tree of length-prefixed elements, and its attachments typically carry the fonts an ASS subtitle track needs. Because it constrains nothing about the streams inside, the extension says nothing about whether a player can decode them. Steve Lhomme started the project in 2002; WebM is the restricted profile of it that browsers accept.
How to use this file
Use an example MKV to test EBML parsing and multi-track demuxing, subtitle and chapter extraction, and remux pipelines, checking that per-track language and default flags survive, that font attachments are preserved, and that a remux to MP4 reports the tracks MP4 cannot carry instead of dropping them silently.
How to use this file for testing
“Multi-Track Audio — Dual Language (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-dual-language.mkv"></video>Related files
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Generated by generation/video_accessibility.py. Free for any use, no attribution required, license.