Multi-Track Subtitles — Two mov_text Tracks (MP4)
Two soft subtitle tracks inside an MP4, in mov_text — the 3GPP Timed Text format that is the only subtitle codec MP4 officially carries. Safari and QuickTime read these natively; most other browsers ignore them entirely and expect a sidecar WebVTT track instead, which is the single most common reason subtitles appear on an iPhone and nowhere else. Compare with the MKV in this group: the cue text is identical, but mov_text drops all styling and positioning, so this is also the file to test a lossy subtitle conversion against.
Browser-playable test video · 8 seconds
Specifications
- Subtitle Tracks
- 2
- Languages
- eng, spa
- Subtitle Codec
- mov_text (3GPP Timed Text / tx3g)
- Default Track
- eng
- Faststart
- true
- Duration
- 8s
Testing contract
Expected to pass- Scenario
- Open the MP4 and enumerate its subtitle tracks.
- Expected result
- 2 mov_text (3GPP Timed Text / tx3g) tracks tagged eng and spa, eng flagged default, faststart enabled, over 8s of video. mov_text is the only subtitle codec MP4 carries portably: remuxing this file to Matroska and back must preserve both tracks and their language tags, while remuxing a Matroska ASS track into MP4 cannot.
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 Subtitles — Two mov_text Tracks (MP4)” is a deterministic Novus Examples fixture for Media accessibility, Subtitle testing, Subtitle parsing, Video QA. 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: 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-mov-text.mp4"></video>Related files
- mkvMulti-Track — Complete Package (MKV)Everything this phase covers in one file: two audio languages, three subtitle tracks including SDH, four chapters, an attached cover image and container tags — with every language tag and disposition set correctly. This is the integration test. The individual fixtures in the other groups isolate one variable each, which is what you want when something breaks; this is what you point a player, a track picker or a transcoder at first, because a pipeline that handles it handles all of them. Round-trip it through your tool and diff the track list: dropped dispositions, collapsed languages and vanished attachments all show up immediately.
- mp4Multi-Track — Complete Package, MP4 Limits (MP4)The same package rebuilt inside MP4, which is the interesting part — MP4 cannot carry all of it. The SDH subtitle track is gone because MP4 has no hearing-impaired flag, the attachment becomes cover art as a second video stream, per-track titles have no home, and the subtitles are mov_text with the styling stripped. Diff this against the MKV in the same group and you have a concrete, byte-level answer to 'what do I lose converting to MP4?' — which is normally something people find out after shipping.
- mkvMulti-Track — Declared but Empty Subtitle Track (MKV)A second subtitle track that is properly declared, correctly language-tagged, and contains no cues at all. This is what an incomplete localisation looks like in a real library: the track exists so the menu offers Spanish, and choosing it produces silence. Track enumeration finds it. Language listing finds it. Only counting the cues finds the problem — which is why 'does this file have Spanish subtitles?' is the wrong question and 'does the Spanish track have any content?' is the right one.
- mkvMulti-Track — Eight Subtitle Tracks (MKV)Eight subtitle tracks across four writing systems, including right-to-left Arabic, each with its own language tag and a track title in its own script. Two things break here that never break with two tracks. Track-picker UI: eight entries is where a fixed-height menu, a truncating label or a hardcoded array bound starts to show. And text rendering: the track titles themselves are non-Latin, so a picker that draws labels with a Latin-only font produces a menu of empty boxes even though every track is perfectly valid.
- mkvMulti-Track — Language Tags Swapped (MKV)Two subtitle tracks whose language tags are swapped: the track tagged `fra` contains English cues and the one tagged `eng` contains French. Nothing about the file is malformed — every byte validates, every tag is a legal ISO 639-2 code. This is the failure no schema check can catch and no player can warn about. Selecting French gives you English, and the only way to detect it is to read the cue text and run language identification on it. If you are building QC for a subtitle library, this is the case worth having a fixture for, because it is common and it is invisible.
- mkvMulti-Track — No Default Flag Anywhere (MKV)Three subtitle tracks and not one of them flagged default. Matroska permits this and players disagree completely about what to do: some pick the first track, some pick by system language, some show nothing at all and leave the viewer to find the menu. There is no right answer to assert here — the value is that the disagreement is reproducible. If your player picks a track, this file tells you which rule it is using.
Generated by generation/video_accessibility.py. Free for any use, no attribution required, license.