Soft Subtitles — MKV (SRT track)
A clip with a soft (muxed, toggleable) SRT subtitle track in a Matroska container — the subtitles are a separate stream, not burned in. A fixture for testing subtitle extraction, rendering, and toggling.
Rendered preview of the mkv file (17.6 KB). Download above for the original.
Specifications
- Resolution
- 480x270
- Fps
- 30
- Duration
- 5s
- Subtitles
- soft SRT (toggleable)
- Codec
- H.264 + SRT
Testing contract
Expected to pass- Scenario
- Decode the clip and confirm its geometry and the event the fixture is named for.
- Expected result
- 480x270 at 30 fps, 5s, H.264 + SRT in Matroska. The clip carries soft SRT (toggleable) subtitles, so a demuxer must report one subtitle stream that can be toggled off without touching the video. The two members of this group carry the same text in the two container-native subtitle codecs, which is what makes a remux between them a meaningful test.
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
“Soft Subtitles — MKV (SRT track)” is a deterministic Novus Examples fixture for Conversion testing. The same content exported across many formats and linked as a group, so you can convert one and diff against the expected twin.
Documented properties for this file: 5s · 30 fps. 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="soft-subtitles.mkv"></video>Related files
- 3gp3GP — Mobile H.264 ClipThe clip as 3GP — the 3GPP mobile container from the feature-phone era. For testing 3GP demuxing and conversion.
- mp460 fps Clip (MP4)A 60 frames-per-second clip with a smoothly sweeping marker — double the usual frame rate. A fixture for testing high-frame-rate playback, frame-rate detection, and fps conversion (60→30 decimation).
- mp4A/V Sync — Beep + Flash (MP4, with audio)A five-second clip that flashes white and plays a 1 kHz beep on every whole second — the first clip in the library WITH an audio track. A direct fixture for measuring and correcting audio/video sync (lip-sync) offset.
- webmAlpha Channel — Opaque VP9 TwinThe same codec and container with NO alpha plane, as the control for the alpha clip in this group. Useful for checking that alpha detection reads the pixel format rather than assuming every WebM is transparent — and for confirming a compositing bug is in the alpha handling rather than in the player.
- webmAlpha Channel — VP9 in WebMVideo with a real per-pixel alpha channel: VP9 yuva420p in WebM, the one alpha path browsers decode natively. Composite it over a page background and the transparency is genuine, not a chroma key. Roughly 90% of each frame is fully transparent. Two traps this file exists to expose. First, auto-alt-ref must be disabled at encode time or libvpx silently drops the alpha plane, producing a valid file with no transparency and no error. Second, WebM stores VP9 alpha in BlockAdditional and signals it with AlphaMode=1, so FFmpeg's NATIVE vp9 decoder reports pix_fmt yuv420p and decodes fully opaque — you must force `-c:v libvpx-vp9` to see the alpha at all. Probing this file with default settings and concluding it has no alpha is the expected mistake.
- assASS — Karaoke Timing and Override TagsAdvanced SubStation Alpha using the features that distinguish it from SubRip: per-syllable \k karaoke timings in centiseconds, a full V4+ style definition with primary and secondary colours, and an \an override that repositions a line. Converting this to SRT necessarily loses all of it, which makes it a good test of whether a converter warns about that or drops it silently.
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