Feature: MPEG-5 LCEVC Scalable support #4572
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Updated references to track to representation
Removed section on shorter buffers for demoing purposes
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@v-nova-romas Thank you for your PR. Can you please merge the latest changes from |
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Hi @dsilhavy Thank you, I have merged the latest changes |
…vcScalableSupport
src/dash/vo/Representation.js
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| @@ -72,6 +72,7 @@ class Representation { | |||
| this.startNumber = 1; | |||
| this.timescale = 1; | |||
| this.width = NaN; | |||
| this.dependentRepresentation = null | |||
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all member attributes in this constructor are sorted alphabetically.
Can you move this new entry?
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Hi @stschr Thank you for taking the time to review the PR!
the new entry should now be sorted alphabetically
| @@ -332,6 +339,9 @@ export default { | |||
| ID3_SCHEME_ID_URI: 'https://aomedia.org/emsg/ID3', | |||
| COMMON_ACCESS_TOKEN_HEADER: 'common-access-token', | |||
| DASH_ROLE_SCHEME_ID : 'urn:mpeg:dash:role:2011', | |||
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| ENHANCEMENT_CODECS: ['lvc1'], | |||
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With this code, 'lvc1' gets always considered as supported by src/streaming/utils/Capabilities.js#L141
However, shouldn't we reject this 4CC if lcevc_dec.js is not registered as extension?
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Thank you, agreed! I would like to modify Capabilities.js#L141 to also check if lcevc_dec.js is loaded, and reject otherwise.
May I ask for clarification regarding registered as extension - is there a way in dash.js to register lcevc_dec.js as a loaded extension? I could check if window.LCEVCdec is defined but I am wondering if there is a more idiomatic way.
| @@ -387,6 +387,9 @@ function CmcdModel() { | |||
| if (mediaType === Constants.AUDIO) { | |||
| ot = CmcdObjectType.AUDIO; | |||
| } | |||
| if (request.mediaType === Constants.ENHANCEMENT) { | |||
| ot = 'e'; | |||
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Maybe not an issue, but where does this magic constant string come from? Is it allowed by Cmcd-spec? (@dsilhavy )
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Originally we have considered that the enhancement doesn't quite fit under existing Cmcd Object Types. However, after looking at the Cmcd-spec it seems that tokens not defined in the spec (eg. e) would be discarded by a Cmcd server.
I would like to assign the enhancement ot to CmcdObjectType.OTHER. Do you think this would be a good approach?
| @@ -646,6 +646,10 @@ function DashManifestModel() { | |||
| voRepresentation.codecs = realRepresentation.codecs; | |||
| voRepresentation.codecFamily = Utils.getCodecFamily(voRepresentation.codecs); | |||
| } | |||
| if (realRepresentation.hasOwnProperty(DashConstants.DEPENDENCY_ID)) { | |||
| voRepresentation.dependentRepresentation = new Representation(); | |||
| voRepresentation.dependentRepresentation.id = realRepresentation[DashConstants.DEPENDENCY_ID].toString(); | |||
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I think we should handle the case when @dependencyId contains multiple @id valeus (as whitespace separated list):
@dsilhavy : What about added this to the capability checks, i.e. rejecting any Representation with more than one entry in this attribute?
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Thank you, great idea! We would like to reject the representation and log it in the console when @dependencyId contains multiple @id values as it would most likely indicate an error with the packager. Do you think this would be a good way to approach it?
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@v-nova-romas Thank you for keeping this PR up to date. As this PR requires design changes in dash.js and I would like to carefully evaluate them, I need to move this PR to the milestone of v5.1. For v5 we have a working sample for LCEVC (https://reference.dashif.org/dash.js/nightly/samples/index.html#MPEG5Part2LCEVC). My apologies for the delay. |
Adds MPEG-5 LCEVC scalable support into dash.js to enable playback of ABR profiles generated by LCEVC enhancement via a separate adaptation set.
This approach creates LCEVC representations which are dependent upon native codec representations (by using dependencyId). LCEVC enhancement representations are contained in a 2nd Adaptation Set and linked to the base representations in the 1st Adaptation Set. The outcome is the ability to play adaptive streaming content where one or more higher resolution profiles are generated by applying LCEVC enhancement to existing conventional profiles saving up to 70% bitrate compared to using conventional standalone native profiles.
There is a new section in dash.js samples for MPEG-5 Part 2 LCEVC where the scalable implementation is demonstrated.