Embedded Metadata — SMPTE Start Timecode (MP4)
A start timecode of 01:00:00:00 — the broadcast convention of beginning programme material at hour one, so that bars, slates and pre-roll can live before it without going negative. FFmpeg writes it as a QuickTime `tmcd` track. The burned-in timecode in the picture deliberately starts at 00:00:00:00 instead. That one-hour disagreement is the whole point: an editor or QC tool that reads the timecode track shows 01:00:00:00 at the first frame, one that reads elapsed time shows zero, and a file where they agree cannot tell you which your tool is doing. Non-drop-frame, since 24 fps has no drop-frame variant.
Browser-playable test video · 8 seconds
Specifications
- Start Timecode
- 01:00:00:00
- Frame Rate
- 24
- Drop Frame
- false
- Storage
- QuickTime tmcd track
- Burned In Timecode Starts At
- 00:00:00:00
- Faststart
- true
- Duration
- 8s
Testing contract
Expected to pass- Scenario
- Open the file, read the start timecode from the container, and compare it against the timecode burned into the picture.
- Expected result
- The container declares a start timecode of 01:00:00:00 at 24 fps, non-drop-frame, in a QuickTime tmcd track - while the burned-in timecode starts at 00:00:00:00. The two deliberately disagree: a tool that reads the picture and a tool that reads the container give different answers, and knowing which one is being read is the point of the fixture.
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
“Embedded Metadata — SMPTE Start Timecode (MP4)” is a deterministic Novus Examples fixture for Media metadata, Video QA, Conversion testing. Video files with embedded chapters, full container tags, attached cover art and a SMPTE start timecode, each paired with a deliberately stripped twin, so you can tell a metadata reader that found nothing from one that was never given anything.
Documented properties for this file: 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-start-timecode.mp4"></video>Related files
- mkvChapters — Embedded in Matroska (MKV)Four named chapters — Cold Open, Titles, Main Segment, Credits — on two-second boundaries. The clip burns the chapter name and a running timecode into the picture, so the chapter marks can be verified by eye against what the player's chapter menu claims. Matroska stores chapters as a proper EditionEntry structure with nanosecond timestamps and per-language names, and every desktop player exposes them. This is the reference case.
- mp4Chapters — Embedded in MP4Four named chapters — Cold Open, Titles, Main Segment, Credits — on two-second boundaries. The clip burns the chapter name and a running timecode into the picture, so the chapter marks can be verified by eye against what the player's chapter menu claims. MP4 has no chapter box. FFmpeg writes them as a QuickTime chapter track — a hidden text track referenced by the video track — which QuickTime, VLC and most desktop players read and which browsers ignore completely. Remux this to MKV and back and the chapters usually survive; convert it with a tool that maps streams individually and they usually do not.
- txtChapters — FFMETADATA1 Chapter FileFFmpeg's own metadata format, and the one used to build the two embedded-chapter files in this group. START and END are integers in the declared TIMEBASE, which is the detail that trips people up: change TIMEBASE and every timestamp silently means something else. This is the exact file the MKV and MP4 chapter fixtures here were built from.
- xmlChapters — Matroska Chapter XMLThe XML dialect `mkvmerge` and `mkvpropedit` read to write chapters into a Matroska file without re-muxing it. Timestamps are nanosecond-precision `HH:MM:SS.nnnnnnnnn`, and each ChapterAtom carries a UID that must be stable across edits — the field most hand-written generators omit, which is why re-running them renumbers every chapter.
- mkvChapters — None (MKV Control)The same clip with the chapter marks explicitly removed. The control for this group, and the file that tells you whether a chapter reader returns an empty list or reports the whole-file duration as a single unnamed chapter — both are common, and they are not the same answer.
- txtChapters — Timestamp List in a DescriptionThe plain-text convention used in video descriptions: `M:SS Title`, one per line, first entry at zero. There is no specification, so every parser guesses — at leading zeros, at `HH:MM:SS` versus `M:SS`, at whether a dash or a dot separates the timestamp from the title. Useful for testing a scraper against the format people actually paste.
Generated by generation/video_accessibility.py. Free for any use, no attribution required, license.