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Dash-Industry-Forum / IOPv5

IOP v5 editing for tracking issues
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need make an order for audio description ,audio preselection , @selectionPriority #25

Open AUGxhub opened 2 years ago

AUGxhub commented 2 years ago

Hello

in short: after check spec from head to tail , there is not a clear order for how to solve following priority related

need a fixed order in spec for those scenarios:

  1. have both audio preselection('urn:mpeg: dash:preselection:2016') and @selectionPriority ,
  2. have both audio description('urn:tva:metadata:cs:AudioPurposeCS:2007' ) , and @selectionPriority ,
  3. have both audio preselection and audio description
  4. have all 3 of above

my suggestion is : take priority from high to low following audio description> audio preselection >@selectionPriority

but still need opinion for this

backgrounds: got some test cases from hbbtv certification(https://eu-app.assembla.com/spaces/HbbTV/subversion/source/HEAD/tags) ,and dolby certification (https://ms12.streaming.dolby.com/v26/app/index.html) which have mixed use of above 3 tags , scenario 1 and 2

looks mainly comes from dolby ac4 cases , need audio related TF check this , maybe @haudiobe ?

B.R Huang Siyuan saber.huang@samsung.net

stschr commented 2 years ago

Hello @AUGxhub

The answer to your question is twofold:

1) On the @selectionPriority attribute: I admit the statement in MPEG-DASH (ISO 23009-1, section 5.3.7.2) is weak:

 "In the absence of other information, higher numbers are the preferred selection over lower numbers."

Here, the import part for your question is contained in the first statement (“In the absence of other information”). But luckily the DVB-DASH specification (ETSI TS 103285) provides clearer guidance on this attribute in clause 10.18:

 “Players  shall only  evaluate the  @selectionPriority  if  no  other differentiation  can  be done based on  existing  attributes and elements  like Role and @lang,  i.e. the  @selectionPriority  attribute  has  the least precendence for selecting  between Preselections.”

IMHO it’s appropriate in this case to assume that both specifications use different words but have the same intent - they are not meant to not contradict each other.

To conclude, the @selectionPriority should be the least dominant decision condition.

This should answer your scenario #2.

2) On the audio preselections: Your text suggests that you refer to the “Preselection Descriptor” according MPEG-DASH, section 5.3.11.2: This descriptor is meant to “indicate that an Adaptation Set is part of a Preselection”. It does NOT provide any indication on the obtained experience thus can’t be prioritized against “audio description” (scenario #3) nor against the @selectionPriority (scenario #1).

Note that Next-Generation Audio typically utilizes the element.