Timed Text Formatting

Validator implements checks to assert conformance to ISO/IEC 14496-30. This is the MP4 subtitle/timed text format.

Should Fix: 14496-12 8.3.2.3 and ISO 14496-30 4.1

tkhd: timed text are normally stacked in front of associated visual tracks layer should therefore be -1.

Should Fix: 14496-30 4.2

Timed text tracks should use suitable language in the mdhd box.

Must Fix: ISO 14496-30 4.2

Samples with a size of zero are not used.

Must Fix: 14496-30 5.4

hdlr is subt for ttml tracks.

Must Fix: 14496-30 Sample Entry

TTML tracks shall use the XMLSubtitleSampleEntry the namespace shall be set to atleast one unique namespace.

Should Fix: 14496-30 5.5 scheme location

The scheme_location field should be set.

Should Fix: 14496-30 5.6 sync samples

Every sample is a sync sample, sync sample table not present.

Must Fix: 14496-30 6.1

VTT Sample boxes shall not contain CR or LF characters, or trailing CRLF sequences.

Must Fix: 14496-30 6.2

Timed text uses nmhd and hdlr is ‘text’.

Must Fix: 14496-30 6.3 sync samples

All samples are sync samples, sync sample table is not used.

Must Fix: 14496-30 6.4 Sample Entry

vtt sample entry is used and correct media handler and nmhd.

Must Fix: 14496-30 6.5 WVTT Sample Entry

In WVTTSampleEntry, WebVTT configuration must occur, containing webvtt file header.

Should Fix: 14496-30 6.5 source label

webvtt source label box should occur in the sample entry.

Must Fix: 14496-30 6.5 Sample

Each sample is either one VTTCueEmptyCueBox or one or more VTTCueBoxes.

Should Fix: 14496-30 6.6 Cue settings

If a cue has WevVTT cue settings they are placed in cue settings box without leading space.

Should Fix: 14496-30 6.6 Cue Source ID

There is no CueSourceIDBox in samples if there is no source label.