Intentionally Corrupt — WebM Truncated Mid-Stream
An intentionally corrupt WebM, VP9 in Matroska, cut to 45% of its bytes. Not a valid file by design. The browser-facing member of this group. A truncated WebM starts playing in an HTML5 <video> element and then fires an `error` event mid-stream, which is a genuinely awkward state to handle: your player has already reported success, already hidden the spinner, and already told the user the duration. Use it to check that the error path is wired to something more useful than a frozen frame.
webm
video/webm
- Integrity
- intentionally corrupt
- Damage
- truncated to 45% of its bytes
- Video Codec
- VP9
- Header Intact
- true
- Original Bytes
- 14237
- Expected Behaviour
- browser fires a media error event partway through playback
Binary webm: no in-browser preview. Download it above to open in a compatible application.
Specifications
- Integrity
- intentionally corrupt
- Damage
- truncated to 45% of its bytes
- Video Codec
- VP9
- Header Intact
- true
- Original Bytes
- 14237
- Expected Behaviour
- browser fires a media error event partway through playback
Testing contract
Expected to fail- Scenario
- Load the file into an HTML5 <video> element and listen for both loadedmetadata and error.
- Expected result
- Metadata loads and playback starts, then the element fires an error event part way through: the file is 6,406 of the original 14,237 bytes of VP9-in-Matroska. The awkward state is the point - the player has already reported success, hidden its spinner and published a duration - so this fixture checks that the error path does something better than freezing on the last decoded frame.
What is a .webm file?
WebM is a deliberately narrow profile of Matroska, restricted to codecs anyone may implement royalty-free. It keeps Matroska's EBML structure but permits only VP8, VP9, or AV1 video with Vorbis or Opus audio, which is what made it the open counterpart to MP4 in an HTML5 `<video>` element. Google announced it at I/O in 2010 alongside the newly open-sourced VP8 and added VP9 and Opus in 2013. That restriction is also its limit: a WebM cannot carry H.264 or AAC at all.
How to use this file
Use an example WebM to test HTML5 `<video>` playback, EBML demuxing, and VP8/VP9 decoding, checking that a converter turning an MP4 into WebM re-encodes rather than attempting a stream copy, since neither H.264 nor AAC has any place in the container.
How to use this file for testing
“Intentionally Corrupt — WebM Truncated Mid-Stream” is a deterministic Novus Examples fixture for Error handling, Video QA, Video codecs. Deliberately corrupt and invalid files, clearly labelled, for testing how your tool fails.
Documented properties for this file: damage: truncated to 45% of its bytes. 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="webm-truncated.webm"></video>Related files
- 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.
- mp4Base Plate — Colour — 24-Patch Chart in MotionA 24-patch chart drifting slowly so it is genuinely moving footage rather than a still. Patch values are fixed and documented, so colourisation and colour-management output can be measured per patch. The values are fictional and not a reproduction of any licensed reference chart. One of eight shared base plates: every AI-video suite in this library degrades one of these rather than inventing its own footage, so results across suites are comparable. Encoded at CRF 14 — well above the house CRF 30 — because a reference compressed as hard as the material under test puts the measurement floor above the effect being measured.
- mp4Base Plate — Gradient — Smooth Sky With Hue DriftA smooth vertical gradient whose hue drifts across the clip, with one soft glow for structure. Almost no high-frequency detail, so it provokes banding and blocking in exactly the way flat skies do in real footage — the hardest case for a low-bitrate encoder. One of eight shared base plates: every AI-video suite in this library degrades one of these rather than inventing its own footage, so results across suites are comparable. Encoded at CRF 14 — well above the house CRF 30 — because a reference compressed as hard as the material under test puts the measurement floor above the effect being measured.
- mp4Base Plate — Text — Scrolling Terminal UIScrolling monospaced terminal output with a blinking cursor. Thin high-contrast glyph edges are what chroma subsampling and low bitrates destroy first, and legibility after processing is a pass/fail signal that needs no metric. One of eight shared base plates: every AI-video suite in this library degrades one of these rather than inventing its own footage, so results across suites are comparable. Encoded at CRF 14 — well above the house CRF 30 — because a reference compressed as hard as the material under test puts the measurement floor above the effect being measured.
- mp4Bitstream — All-Intra (Every Frame a Keyframe)Every frame is an I-frame, so any frame is an independent cut point. Much larger, and the shape editing and frame-accurate seeking want. Same picture and same codec as every other clip in this group — only the GOP and frame-type structure differ, so the effect on size and seekability is directly attributable.
Generated by generation/video_accessibility.py. Free for any use, no attribution required, license.