webm1.9 KB

Creator Overlay Alpha WebM 005

VP9 WebM overlay clip 005 with a transparent canvas and moving semi-transparent marks for compositing tests. Stable P8 artifact p8-video-overlay-webm-005.

Video editing Video QA Media pipeline testing

Browser-playable test video · 0.750 seconds

Specifications

Variant: 205
Codec: VP9
Resolution: 192x108
Fps: 12
Has Alpha: true
Delivery Mode: browser-playable
Measured Duration Seconds: 0.75
Duration Measurement: ffprobe format.duration after asset write
Provider: browser-local
Provenance: Synthetic deterministic P8 fixture generated by generation/p8_content.py; seed namespace 2026082300

Testing contract

Expected to pass

Scenario: Decode every frame of p8-video-overlay-webm-005 in a browser-capable WEBM demuxer and compare the duration with the P8 measurement ledger.
Expected result: The WEBM decodes at 192x108 and 12 fps, reports 0.75 seconds within 0.01, and preserves the moving frame marker for variant 205.

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

“Creator Overlay Alpha WebM 005” is a deterministic Novus Examples fixture for Video editing, Video QA, Media pipeline testing. Short playable clips plus overlays, captions, timelines, colour targets, sync references, and controlled failures for testing browser and desktop editing workflows.

Documented properties for this file: 12 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.

Playable creator clips use their measured duration and catalog thumbnail on a watch-first page. Timeline, caption, sync, colour, and failure sidecars remain download-only; compare their ordered decisions and expected outcome rather than assuming every creator format is browser-playable.

Relink the declared local assets, preserve rational or frame-based timing, and compare the resulting clip order, transitions, duration, and sync markers with the expected contract.

Code examples

<video controls preload="metadata" width="640" src="p8-video-overlay-webm-005.webm"></video>

Generated by generation/p8_content.py. Free for any use, no attribution required — license.