Add subtitle->audio track linking #471
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| @@ -454,6 +454,12 @@ the overlay track **SHOULD** be used instead. The order of multiple TrackOverlay | |||
| If not found it **SHOULD** be the second, etc.</documentation> | |||
| <extension type="webmproject.org" webm="0"/> | |||
| </element> | |||
| <element name="TrackLink" path="\Segment\Tracks\TrackEntry\TrackLink" id="0x6FAC" type="uinteger"> | |||
| <documentation lang="en" purpose="definition">Specify that subtitle track is suitable for use with the audio Track UID specified (in the u-integer). | |||
| Multiple subtitle tracks may link to the same audio track, and the same subtitle track may link to multiple audio tracks by providing multiple TrackLink elements. | |||
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It should mention that the TrackEntry it belongs to **MUST** be a subtitle track, in a normative way.
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| Track links are only necessary when the set of tracks available creates ambiguity about which | ||
| subtitles are appropriate for which audio, and function as a hint to the player to improve | ||
| its automatic track selection behavior. In cases where there is no such ambiguity, there is |
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There should be a link to the (#default-track-selection) section here. And probably augment the "Subtitle selection" section on how to use the TrackLink to solve such ambiguity.
robUx4
added
format addition
matroska-v5
spec_codecs
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The Given there's probably 0 use anywhere in the wild of this feature I don't mind the change. We may also change the name to Now given all of these are unused we might as well mark them as deprecated so they are not used while not specified properly or are of any use to anyone. This feature is basically used to replace parts of a track by another track the container level. This can be useful in video to encode a whole movie normally and have some parts with translated text on the video encoded in different tracks. But then it says the overlay picks the first available track, so I don't know how this can be of any use. Maybe silently replacing parts of a video that have been removed by another part without reencoding, maybe even using a different codec. In this scenario the multiple For the |
Useful for cases where the appropriate tracks are otherwise ambiguous; see added notes.md section for a few examples.
Also clarified that
TrackOverlayrefers to tracks by their UIDs rather than their numbers; as far as I can tell this is the intent, but I can't find anything existing confirming this either way (nor any implementation code), so I could be wrong, but it seems consistent with other elements.Previously it was suggested that
TrackLinkshould go in a dedicated container element with maxOccurs=1, but I don't see any particular technical reason for that, andTrackOverlayalready allows multiple instances without a container, though I can add one if that's a policy for newly-added elements or something.