Multi-Track Audio — Single Mono Track (MP4)
One mono audio track — the shape most phone recordings, voice notes and screen captures actually arrive in, and the one that catches pipelines that hardcode a stereo buffer or index channel 1 without checking that it exists.
Browser-playable test video · 8 seconds
Specifications
- Audio Tracks
- 1
- Channels
- 1
- Channel Layout
- mono
- Tone
- 440 Hz
- Codec
- AAC LC 64 kbps 48 kHz
- Faststart
- true
- Duration
- 8s
Testing contract
Expected to pass- Scenario
- Open the file and read its channel count and layout.
- Expected result
- 1 AAC LC track at 48 kHz, 1 channel, mono layout, carrying a 440 Hz tone, faststart, 8s. It is the counterpart to the 5.1 member of this group: code that assumes stereo and indexes channel 1 fails here, and code that assumes a fixed channel count fails on one or the other.
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
“Multi-Track Audio — Single Mono Track (MP4)” is a deterministic Novus Examples fixture for Media accessibility, Video QA, Video codecs, Conversion testing. Containers carrying several subtitle and audio tracks at once, with real language tags and the default, forced, hearing-impaired and visual-impaired flags actually set, for testing track pickers, accessibility menus, and the flag handling that only shows up when more than one track exists.
Documented properties for this file: 1 ch · 8s. 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="mp4-mono.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.
- 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.
Generated by generation/video_accessibility.py. Free for any use, no attribution required, license.