Countdown with Timecode (MP4)
A six-second countdown (5→0) with a sweeping second-arc, a burned-in SS:FF timecode, and a beep on each second — a slate/leader fixture for testing timecode reading, frame-accurate seeking, and sync.
Browser-playable test video · 6 seconds
Specifications
- Resolution
- 480x270
- Fps
- 30
- Duration
- 6s
- Timecode
- SS:FF burned in
- Audio
- beep each second
- Codec
- H.264 + AAC
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, 6s, H.264 + AAC in MP4. A SS:FF burned in timecode is burned into the picture and the audio carries a beep each second. The burned-in timecode is readable from a single extracted frame, which makes frame-accurate seeking checkable without decoding the whole clip.
What is a .mp4 file?
MP4 (MPEG-4 Part 14) is the dominant container for digital video, holding video, audio, subtitle, and metadata tracks in a tree of typed boxes. `ftyp` declares the brand, `moov` carries the sample tables that make seeking possible, and `mdat` holds the media; when an encoder writes `moov` last, playback cannot begin until the file has fully downloaded, which a faststart remux fixes. It derives from Apple's QuickTime format, generalized by ISO into the ISOBMFF base that MOV, 3GP, and HEIF share.
How to use this file
Use an example MP4 to test box parsing and track detection, seeking, range-request streaming, and transcode or thumbnail pipelines — verifying that a file with a trailing `moov` box is still handled, and that codec support is checked per track rather than inferred from the extension.
How to use this file for testing
“Countdown with Timecode (MP4)” 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: 6s · 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="countdown-timecode.mp4"></video>Related files
- mp4SMPTE Colour Bars + 1 kHz Tone (MP4)Standard SMPTE-style colour bars with a 1 kHz reference tone — the classic broadcast test pattern. A fixture for calibrating colour, testing decoders, and verifying audio alongside a known video signal.
- 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.
Generated by generation/video_realistic.py. Free for any use, no attribution required — license.