Alpha Channel — Opaque VP9 Twin
The 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.
Specifications
- Resolution
- 480x270
- Fps
- 24
- Codec
- VP9 (libvpx-vp9)
- Pixel Format
- yuv420p — no alpha plane
- Container
- WebM
What is a .webm file?
WebM is an open, royalty-free multimedia container based on Matroska, designed for the web and typically carrying VP8 or VP9 video with Vorbis or Opus audio. It is natively supported by modern browsers via HTML5 video. It targets efficient, license-free web streaming.
How to use this file
Use an example WebM to test HTML5 <video> playback, Matroska-based demuxing, VP8/VP9 decoding, and converters between WebM and MP4.
How to use this file for testing
“Alpha Channel — Opaque VP9 Twin” is a deterministic Novus Examples fixture for Video codecs, Conversion testing, Video QA. One source encoded as H.264, HEVC, AV1, VP9, MJPEG, and a ProRes-compatible mezzanine, across 8/10/12-bit and 4:2:0/4:2:2/4:4:4 — for testing decoder support, transcode pipelines, and container remuxing.
Documented properties for this file: 24 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="vp9-opaque.webm"></video>Related files
- 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.
- mp4Bitstream — Heavy B-Frames (8 Consecutive)Eight consecutive B-frames with a B-pyramid, so decode order and display order diverge sharply and DTS runs well behind PTS. The case that breaks naive timestamp handling and any code that assumes frames arrive in display order. 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.
- mp4Bitstream — Long GOP (24 Frames, One Per Second)One keyframe per second — the delivery default, and the setting that determines HLS/DASH segment boundaries, since a segment must start on a keyframe. 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.
- mp4Bitstream — No B-FramesI and P frames only. Required by some low-latency and legacy decoders, and it removes the reordering that makes decode order differ from display order. 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.
- mp4Bitstream — Short GOP (8 Frames)A keyframe every 8 frames with scene-cut detection disabled, so the GOP length is exactly what it says. Short GOPs cost bitrate but bound seek latency — the trade-off streaming packagers make explicitly. 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.
- mp4Bitstream — Single GOP (One Keyframe Only)Exactly one keyframe, at the start. Maximally efficient and nearly unseekable: a player must decode from frame zero to reach any position, which is what makes long-GOP archives painful to scrub. 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_codecs_wave.py. Free for any use, no attribution required — license.