MP4 TTML segments with multiple samples are not correctly handled #8087
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component: TTML
The issue involves TTML subtitles specifically
priority: P1
Big impact or workaround impractical; resolve before feature release
type: bug
Something isn't working correctly
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julijane
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Feb 15, 2025
Fixes shaka-project#8087 Implements handling of multiple samples in a segment. Also fixes the testdata for the multiple MDAT test, as the prior data was invalid (not conforming to ISO14496-12).
julijane
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Feb 15, 2025
Fixes shaka-project#8087 Implements handling of multiple samples in a segment. Also fixes the testdata for the multiple MDAT test, as the prior data was invalid (not conforming to ISO14496-12).
theodab
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component: TTML
julijane
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Feb 15, 2025
Fixes shaka-project#8087 Implements handling of multiple samples in a segment. Also fixes the testdata for the multiple MDAT test, as the prior data was invalid (not conforming to ISO14496-12).
julijane
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Feb 17, 2025
Fixes shaka-project#8087 Implements handling of multiple samples in a segment. Also fixes the testdata for the multiple MDAT test, as the prior data was invalid (not conforming to ISO14496-12).
julijane
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Feb 17, 2025
Fixes shaka-project#8087 Implements handling of multiple samples in a segment. Also fixes the testdata for the multiple MDAT test, as the prior data was invalid (not conforming to ISO14496-12).
avelad
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Feb 17, 2025
Fixes #8087 Implements handling of multiple samples in a MP4/ISOBMFF/DASH TTML segment/fragment. Such segments are allowed by ISO14496-12 and ISO23000-19. gpac creates such segments. The prior code just treated the full MDAT as one TTML XML document and tried to parse it in whole without accounting for sample(s). A testcase is included which was created by taking the testdata from ttml-segment.mp4 and splitting the subtitles into two independent TTML-XML documents, which then were put as individual samples. The testdata for the prior existing multiple MDAT testcase was invalid. It was created by taking the same ttml-segment.mp4 as a source and just duplicating the MDAT box, but without then also fixing the TRUN box. The duplicated data was thus not referenced. The test case still worked, because the prior code did not look at the TRUN box and the sample specification at all and just handled any full MDAT box = 1 sample. The testdata was replaced with a new file, which is basically the same as for the multiple samples case, but with the two samples split into two MDAT boxes.
avelad
pushed a commit
that referenced
this issue
Feb 17, 2025
Fixes #8087 Implements handling of multiple samples in a MP4/ISOBMFF/DASH TTML segment/fragment. Such segments are allowed by ISO14496-12 and ISO23000-19. gpac creates such segments. The prior code just treated the full MDAT as one TTML XML document and tried to parse it in whole without accounting for sample(s). A testcase is included which was created by taking the testdata from ttml-segment.mp4 and splitting the subtitles into two independent TTML-XML documents, which then were put as individual samples. The testdata for the prior existing multiple MDAT testcase was invalid. It was created by taking the same ttml-segment.mp4 as a source and just duplicating the MDAT box, but without then also fixing the TRUN box. The duplicated data was thus not referenced. The test case still worked, because the prior code did not look at the TRUN box and the sample specification at all and just handled any full MDAT box = 1 sample. The testdata was replaced with a new file, which is basically the same as for the multiple samples case, but with the two samples split into two MDAT boxes.
joeyparrish
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Feb 22, 2025
Fixes #8087 Implements handling of multiple samples in a MP4/ISOBMFF/DASH TTML segment/fragment. Such segments are allowed by ISO14496-12 and ISO23000-19. gpac creates such segments. The prior code just treated the full MDAT as one TTML XML document and tried to parse it in whole without accounting for sample(s). A testcase is included which was created by taking the testdata from ttml-segment.mp4 and splitting the subtitles into two independent TTML-XML documents, which then were put as individual samples. The testdata for the prior existing multiple MDAT testcase was invalid. It was created by taking the same ttml-segment.mp4 as a source and just duplicating the MDAT box, but without then also fixing the TRUN box. The duplicated data was thus not referenced. The test case still worked, because the prior code did not look at the TRUN box and the sample specification at all and just handled any full MDAT box = 1 sample. The testdata was replaced with a new file, which is basically the same as for the multiple samples case, but with the two samples split into two MDAT boxes. Backported to v4.9.x
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Have you read the FAQ and checked for duplicate open issues?
yes
If the problem is related to FairPlay, have you read the tutorial?
n/a
What version of Shaka Player are you using?
v4.13.2
Can you reproduce the issue with our latest release version?
yes
Can you reproduce the issue with the latest code from
main?yes
Are you using the demo app or your own custom app?
custom app
If custom app, can you reproduce the issue using our demo app?
not tried, but as the issue is clearly not implemented handling logic, there is no need to
What browser and OS are you using?
Chrome on Linux, not that it matters.
For embedded devices (smart TVs, etc.), what model and firmware version are you using?
n/a
What are the manifest and license server URIs?
n/a
What configuration are you using? What is the output of
player.getNonDefaultConfiguration()?n/a
What did you do?
Attempted to playback a DASH presentation which has a caption track where the segments have multiple samples. This is allowed as per ISO14496-12 and ISO23000-19. gpac creates such segments.
What did you expect to happen?
Subtitles to be displayed.
What actually happened?
Errors in the console about not being able to parse the TTML XML.
Are you planning to send a PR to fix it?
yes, the fix is already implemented.
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