Intentionally Corrupt — Matroska Bytes With an .mp4 Extension
An intentionally corrupt fixture of a different kind: the bytes are a perfectly valid Matroska file, and the extension says `.mp4`. Nothing is damaged — the file simply lies about what it is. Not a valid MP4 by design. This is what a user's 'converted' file usually turns out to be after a rename, and it separates two kinds of code cleanly. Anything that sniffs the first four bytes finds `1A 45 DF A3`, identifies EBML and plays it. Anything that dispatches on the extension hands it to an MP4 demuxer that immediately fails to find `ftyp`. Note the catalog records this entry's MIME as video/mp4, matching the extension rather than the content — deliberately, because that is precisely the mismatch being reproduced.
mp4
video/mp4
- Integrity
- intentionally corrupt — mislabelled, not damaged
- Actual Format
- Matroska
- Declared Extension
- .mp4
- Magic Bytes
- 1A 45 DF A3 (EBML) — not ftyp
- Playable
- yes, by anything that sniffs content rather than trusting the name
- Bytes
- 12347
Binary mp4 — no in-browser preview. Download it above to open in a compatible application.
Specifications
- Integrity
- intentionally corrupt — mislabelled, not damaged
- Actual Format
- Matroska
- Declared Extension
- .mp4
- Magic Bytes
- 1A 45 DF A3 (EBML) — not ftyp
- Playable
- yes, by anything that sniffs content rather than trusting the name
- Bytes
- 12347
What is a .mp4 file?
MP4 (MPEG-4 Part 14) is a widely supported multimedia container based on ISOBMFF that holds video, audio, subtitles, and metadata, most commonly H.264 or H.265 video with AAC audio. It supports streaming, chapters, and multiple tracks. It is the dominant format for distributing and playing digital video.
How to use this file
Use an example MP4 to test container demuxing, track and codec detection, seeking and streaming, and transcoding or thumbnail-extraction pipelines.
How to use this file for testing
“Intentionally Corrupt — Matroska Bytes With an .mp4 Extension” 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: MP4 · 12,347 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="matroska-renamed-as-mp4.mp4"></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.