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https://www.w3.org/TR/2021/WD-imsc-hrm-20211109/

w3c/imsc-hrm#6
w3c/imsc-hrm#3
w3c/imsc-hrm#4
w3c/imsc-hrm#2

The codepoint sets used in determining GCpy fail to include entries in http://www.unicode.org/Public/UNIDATA/Scripts.txt that do not include a range.

The render time and glyph cache checks do not tolerate any numerical errors:

When processing an MP4 file list, if an init file (filename with "init" in it) is omitted, the error message is: "error XML parsing error: not well-formed (invalid token): line 1, column 0", which appears as if it is processing a text (xml) file. It would be better if the message was something like "required init file is missing".

Netflix timing guidelines for subtitles recommends to "close the gap" between subtitles when the gap is smaller than 500ms by setting the gap to 2 frames.

This means that the validation fails on perfectly acceptable documents that produce an ISD sequence with short, empty ISD documents in between long-duration, non-empty ISD documents. The software (and maybe the spec) should be updated to work with such documents.

Right now, the imsc-hrm-tests dur003-fail passes when it should fail. See also w3c/imsc-hrm-tests#9.

It used to fail in imscHRM because the previous ISD beginning at 2.5s was considered non-empty, and therefore made the available time for the following ISD beginning at 3s be 0.5s. However, that previous ISD only contained content not associated with any region, and should therefore have been pruned. If it had been pruned, then the ISD should have been considered empty, and therefore the ISD beginning at 3s would have had a full 1s to render, and that older variant of the test should have passed instead of failing.

_compute_dur_t() is called on empty ISDs and always invalidates the glyph cache.

The unit test fixture will not catch an expected-to-fail test that, in fact, does not fail the HRM:

This is a relatively common message which produces no output. Most often there is a problem with the file, perhaps the ISOBMFF segment (the containing IMSC1 document validates). Some hint about what was not liked is important to proceeding.

Test file provided privately.