MP4 — Audio Desync 250ms
SAMPLE clip with audio delayed ~250 ms — for A/V sync detection tools.
Browser-playable test video · 2.500 seconds
Specifications
- Fps
- 24
- Codec
- H.264
- Container
- MP4
- Wave
- G
- Resolution
- 480x270
- Audio Delay Ms
- 250
- Duration
- 2.50s
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 24 fps, 2.50s, H.264 in MP4. The audio is delayed by 250 ms relative to the video. The offset is exact and known, so an A/V-sync measurement can be scored rather than eyeballed, and the three delays in this group bracket the roughly 45 ms threshold at which lip-sync error becomes perceptible.
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
“MP4 — Audio Desync 250ms” is a deterministic Novus Examples fixture for Conversion testing, Audio analysis. 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: 2.50s · 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="desync-250ms.mp4"></video>Related files
- mp4MP4 — A/V Mux with 440 Hz ToneVideo muxed with a 440 Hz sine tone — for A/V container and audio-track tests.
- mp4MP4 — A/V Mux with 880 Hz ToneVideo muxed with an 880 Hz tone — frequency twin for audio pipeline tests.
- 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.
- mp4MP4 — Colour Bars + 1 kHz ToneSMPTE-ish colour bars with a 1 kHz reference tone — classic QC fixture.
- 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.
- wav1 kHz Tone @ 16000 Hz Sample Rate (WAV)A 1 kHz sine tone sampled at 16000 Hz — part of a sample-rate ladder (8/16/44.1/48/96 kHz) of the identical tone, for testing resampling, sample-rate detection, and aliasing.
Generated by generation/video_wave_g.py. Free for any use, no attribution required, license.