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6.1 Common DASH Specific Aspects for Audio
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6.1.1 Adaptation Sets and Representations
All audio Representations except for those that refer to NGA Auxiliary Audio streams shall either define or inherit the elements and attributes shown in Table 4. ETSI ETSI TS 103 285 V1.3.1 (2020-02) 31 Table 4: Mandatory Elements and Attributes For All Representations within an Audio Adaptation Set Parameter Descripti...
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6.2 DASH Specific Aspects for HE-AACv2 Audio
The profile for basic stereo audio support shall be the MPEG-4 High Efficiency AAC v2 Profile, level 2 which also means that Players will be able to play AAC-LC, HE-AAC and HE-AACv2 encoded content. When using HE-AAC and HE-AACv2 bitstreams, explicit backwards compatible signalling shall be used to indicate the use of ...
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6.3 DASH Specific Aspects of Dolby Audio Technologies
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6.3.1 DASH specific aspects of Enhanced AC-3 and AC-4 part 1
The signalling of the different audio codecs and the ISO BMFF encapsulation is in Table 8. Table 8: Codec Parameters and ISO BMFF encapsulation Codec MIME type @codecs attribute ISO BMFF Encapsulation SAP Type Enhanced AC- 3 audio/mp4 ec-3 ETSI TS 102 366 [10], annex F 1 AC-4 audio/mp4 ac-4.aa.bb.cc ETSI TS 103 190-1 [...
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6.3.2.1 ETSI TS 103 190-1 and ETSI TS 103 190-2
AC-4 is defined by means of a multipart specification, ETSI TS 103 190-1 [23] and ETSI TS 103 190-2 [33]. Information from the configuration records of the bit stream, i.e. the decoder specific information (DSI), shall be used to set parameter that are relevant for indication of AC-4 in manifests: • For AC-4 bitstream_...
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6.3.2.2 AC-4 for channel-based, immersive and personalized audio
The coding and decoding of the raw AC-4 frames of an AC-4 elementary stream is defined in ETSI TS 103 190-2 [33]. AC-4 elementary streams consist of presentations, which define a set of one or more substream groups to be presented simultaneously. ETSI TS 101 154 [3] defines additional requirements and constraints on AC...
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6.3.2.3 DRC and Loudness
Requirements on DRC and Loudness processing apply as described in ETSI TS 101 154 [3], clause 6.7.5.
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6.3.2.4 Dialogue Enhancement
Requirements on Dialogue Enhancement apply as described in ETSI TS 101 154 [3], clause 6.7.6. 6.3.2.5 Additional Constraints for Packaging of Individual AC-4 Audio Programme Components into ISO BMFF In MRMP use-cases, the following constraints shall apply to all contributing Main and auxiliary NGA streams: • The durati...
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6.3.2.6 DASH Element and attribute settings for AC-4
Table 9 provides the details on how AC-4 and related parameters are signalled with DASH elements and attributes that can be used on Adaptation Sets as well as on Preselection elements unless explicitly indicated. Table 9: AC-4 Elements and Attributes settings Element or Attribute Name Description @codecs For AC-4 the v...
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6.3.3 Additional requirements for AC-4 encapsulation into ISO BMFF
The following additional constraints shall apply when packaging AC-4 audio into Representations of an Adaptation Set for DASH: • The value of the frame_rate_index parameter shall remain constant within each Representation. • The value of the presentation_config parameter shall remain constant within each Representation...
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6.4 DASH Specific Aspects of DTS Audio Technologies
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6.4.1 General requirements for DTS media formats
The signalling of DTS audio formats using ISO BMFF encapsulation is provided in Table 10. Table 10: DTS Audio Technologies: Codec Parameters and ISO BMFF encapsulation Codec MIME type @codecs attribute ISO BMFF Encapsulation SAP Type DTS core audio/mp4 dtsc ETSI TS 102 114 [11], Annex E 1 DTS-HD (with legacy core) audi...
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6.4.2 Additional Guidelines for DTS-UHD formats
For DTS-UHD, two profiles are defined. Profile 2 uses the compression algorithms defined in ETSI TS 103 491 [42] to implement a traditionally formatted audio program (non-NGA) with greater flexibility and efficiency. A profile 2 bitstream contains a channel-based presentation with up to nine full bandwidth channels and...
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6.5 DASH Specific Aspects of MPEG Surround
MPEG Surround, as defined in ISO/IEC 23003-1 [12], is a scheme for coding multichannel signals based on a down-mixed signal of the original multichannel signal, and associated spatial parameters. The down-mix shall be coded with MPEG-4 High Efficiency AAC v2 according to clause 6.2. MPEG Surround shall comply with leve...
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6.6 Service Continuity Considerations
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6.6.1 Introduction
Scaling the bit rate for maintaining service continuity under difficult network conditions is a key feature of DASH. In many situations it is sufficient to just scale the video bit rate. However, if the bit rate is severely constrained, it can be advantageous to also scale the audio bit rate as well in order to balance...
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6.6.2 Default Operation for Seamless Service Continuity
In order to allow service continuity with seamless bit rate adaptation it is recommended that the audio Adaptation Set used for main service operation includes Representations from the lowest required bit rate. If the service wishes to support bit rates below 96 kbps then it is recommended that the Player supports a su...
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6.6.3 Fallback Operation
If the audio codec used for main service operation does not provide sufficient capability to scale down bit rates low enough within an Adaptation Set, an additional audio Adaptation Set should be provided within the DASH presentation. Adaptation sets with the purpose of providing media streams with low bit rates for fa...
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6.7 Signalling of NGA Preselections
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6.7.1 Introduction
This clause describes the signalling for next generation audio (NGA) formats in the manifest, based on DASH Preselections. It covers the following NGA codecs: • AC-4 • DTS-UHD • MPEG-H Audio 6.7.2 Content Creation Options and Use of the DASH Preselection Element The NGA formats support the concept of component based au...
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6.7.3 Signalling Audio Properties for DASH Preselections
DASH clients supporting SRMP or MRMP audio shall support the signalling of Preselections by means of Preselection elements. This is for bit stream configurations where multiple personalization options are available from one elementary stream (SRMP), or where multiple streams contribute to multiple personalization optio...
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6.7.4 Use of the Role Scheme to Distinguish between Preselections
Every NGA Preselection element shall include at least one Role element using the scheme "urn:mpeg:dash:role:2011" as defined in ISO/IEC 23009-1 [1]. The use of the @value attribute set to "main" for audio content indicates that the Preselection is the preferred audio Preselection by the content provider. If there is on...
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6.7.5 Accessibility Signalling with Preselection Elements
Preselection elements which enable accessibility features shall be signaled with a Role and Accessibility element according to Table 12. Table 12: Role and Accessibility elements for Audio Description and Clean Audio contained in Preselection element Description Role element element Accessibility element Broadcast Mix ...
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6.7.6 Example configurations using DASH Preselections Elements
Signalling of audio properties like codec, language, or accessibility features in DASH is done based on specific attributes and descriptors indicated on Preselection elements. The examples in Table 13 illustrate the signalling for the SRMP use-cases and the examples in Table 15 illustrate the signalling for the MRMP us...
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6.8 DASH Specific Aspects of MPEG-H Audio
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6.8.1 Introduction
This clause describes the requirements for encoding, packaging and signalling of MPEG H Audio. The bit-stream described is equivalent to the bit-stream description given in clause 6.8 of ETSI TS 101 154 [3] with minor modifications to take into account the packaging in ISO BMFF containers. A more detailed introduction ...
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6.8.2 MPEG-H Audio Elementary Stream Requirements
The elementary stream requirements are defined in clause 6.8.2 of ETSI TS 101 154 [3].
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6.8.3 Storage of MPEG H Audio Media Samples
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6.8.3.1 Bit Stream Encapsulation
The bit stream encapsulation is defined in clause 6.8.3 in ETSI TS 101 154 [3]. In addition, the following additional constraints apply. The following packet types may be present in the bit-stream but there is no requirement of them to be parsed by players: • PACTYP_SYNC • PACTYP_SYNCGAP Use Case 2 (AC-4) Adaptation Se...
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6.8.3.2 ISO BMFF packaging and segmentation
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6.8.3.2.1 Introduction
The carriage of MPEG-H Audio in the ISO BMFF file format is specified in ISO/IEC 23008-3 [34], clause 20. This clause provides constraints on how MHAS shall be packetized and signalled in ISO BMFF.
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6.8.3.2.2 MPEG-H Audio Sample Entry
The sample entry "mhm1" shall be used in cases of SRSP and SRMP for encapsulation of MHAS packets into ISO BMFF segments, according to ISO/IEC 23008-3 [34], clause 20.6. The sample entry "mhm2" shall be used in cases of MRMP as described in ISO/IEC 23008-3 [34], clause 14.6.
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6.8.3.2.3 MHAConfigurationBox
If the MHAConfigurationBox() is present, the MPEG-H Audio profile and level indicator mpegh3daProfileLevelIndication in the MHADecoderConfigurationRecord() shall be set to "0x0B", "0x0C", or "0x0D" for MPEG-H Audio LC Profile Level 1, Level 2, or Level 3, respectively. The parameters carried in the MHADecoderConfigurat...
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6.8.3.2.4 Random Access Point and Stream Access Point
A sync sample is a random access point (RAP) as defined in clause 6.8.4.1 of ETSI TS 101 154 [3]. In addition, the following constraints apply: • A PACTYP_SYNC MHAS packet should not be included Therefore, a sync sample consists of the following MHAS packets, in the following order: • PACTYP_MPEGH3DACFG • PACTYP_AUDIOS...
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6.8.3.2.5 Configuration Change Constraints
The configuration change constraints are defined in clause 6.8.5 of ETSI TS 101 154 [3]. ETSI ETSI TS 103 285 V1.3.1 (2020-02) 46 The following additional constraints apply: • A configuration change may happen at the beginning of a new ISO BMFF segment or at any position within the segment. In the latter case, the File...
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6.8.3.2.6 MPEG H Audio Multi-Stream Constraints
The MPEG-H Audio multi-stream constraints are defined in clause 6.8.7 of ETSI TS 101 154 [3]. In addition, the following constraint applies: • For the MRMP use case, the ISO BMFF segments shall use the sample entry "mhm2" NOTE: Representations that belong to one Adaptation Set need to use different MHASPacketLabel valu...
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6.8.3.2.7 Audio Preselection Constraints
If the Audio Programme contains an audio Preselection description, the audio Preselection constraints are defined in clause 6.8.6 of ETSI TS 101 154 [3].
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6.8.3.2.8 Loudness and Dynamic Range Control
Loudness and dynamic range control is defined in clause 6.8.8 of ETSI TS 101 154 [3].
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6.8.4 DASH Element and Attribute Settings for MPEG-H Audio
The attributes and elements listed in Table 17 can be used on AdaptationSets as well as on Preselection elements unless explicitly indicated. Table 17: MPEG-H Audio programme components and Attributes Element or Attribute Name Description @codecs For MPEG-H Audio, the value of the codecs attribute shall be created acco...
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7 DASH Specific Aspects for Subtitles
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7.1 Carriage of Subtitles
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7.1.1 General
Where provided, subtitles shall be formatted using the EBU-TT-D Subtitling Distribution Format as specified in EBU Tech 3380 [13] and encapsulated in ISO BMFF in accordance with Carriage of EBU-TT-D in ISO BMFF specified in EBU Tech 3381 [14]. Where the subtitles require or may require the downloading of fonts, these s...
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7.1.2 Distinguishing Between Different Uses of Subtitles
Subtitles are used to provide text which is synchronized to other media components and can be displayed on screen for the viewer. There are a number of scenarios in which subtitles might be used, for example to provide: • access services - typically subtitles for the hard of hearing, which contain both a transcript of ...
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7.2 Downloadable fonts
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7.2.0 Introduction
This clause defines a mechanism by which the availability of downloadable fonts may be signalled using descriptors within the MPD, the format of fonts made available and requirements on Players to support these.
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7.2.1 Signalling within the MPD
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7.2.1.1 DVB font download scheme
The availability of downloadable fonts is signalled using the EssentialProperty or SupplementalProperty descriptor. This descriptor shall use the values for @schemeIdUri and @value specified in clause 7.2.1.2. The descriptor shall carry all the mandatory additional attributes defined in clause 7.2.1.3. A descriptor wit...
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7.2.1.2 Scheme Identification in descriptors
A descriptor is signalling a downloadable font in accordance with the present document when it has the @schemeIdUri attribute set to "urn:dvb:dash:fontdownload:2014" and the @value attribute set to 1. 7.2.1.3 Additional attributes on the EssentialProperty and SupplementalProperty descriptors The following attributes ar...
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7.2.2 Font format
Fonts for download shall be provided in one of the formats listed in Table 21. The mime type used in the descriptor shall be the appropriate one from Table 21. Table 21: Supported font formats and their corresponding mime types Font Format Mime Type to specify in @mimeType attribute Open Font Format specified in ISO/IE...
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7.2.3 Errors
If a Player is unable to download a font for any reason or having downloaded a font is unable to process it, then: • If the font download was signalled using the EssentialProperty descriptor, the Adaptation Set containing the descriptor shall not be presented. • If the font download was signalled using the Supplemental...
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7.2.4 Player support
Players should support the downloading of fonts which are contained in the formats specified in clause 7.2.2 and are signalled using the mechanism in clause 7.2.1. Players which do not support the downloading of fonts shall follow the rules in clause 7.2.1.1 regarding the action to take depending upon the descriptor us...
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7.3 Example (informative)
The following extract from an MPD shows an Adaptation Set being used to deliver English subtitles for the hard of hearing where the main programme audio is in English and the content provider is making available a font to download. <AdaptationSet id="sub1" startWithSAP="1" mimeType="application/mp4" lang="eng" codecs="...
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8 Content Protection
8.1 Introduction The DVB MPEG DASH profile does not specify a full end-to-end content protection system (DRM), rather it specifies the usage of specific parameters that are defined within the MPEG DASH (ISO/IEC 23009-1 [1]) MPD and within the ISO Common Encryption "CENC" (ISO/IEC 23001-7 [7]). This enables multiple DRM...
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8.2 Background (informative)
Media protected according to ISO/IEC 23001-7 [7] may require DRM specific information to decrypt. ISO/IEC 23001-7 [7] defines a Protection System Specific Header ('pssh') box to carry this information. The DRM is identified thanks to the SystemID parameter in the 'pssh'. MPEG DASH also allows the carriage of DRM specif...
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8.3 Encryption of Different Representations
All Representations in the same Adaptation Set shall be protected by the same license, and encrypted with the same key. That means all Representations shall have the same value of 'default_KID' in their 'tenc' boxes in their Initialization Segments. That also means that the ContentProtection descriptor shall be placed ...
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8.4 MPEG DASH MPD Content Protection descriptors
Players shall be able to process ContentProtection descriptors from the MPD. Players may ignore ContentProtection descriptors with @schemeIdUri attribute values that they do not understand. Any Adaptation Set containing protected content shall contain one "mp4protection" ContentProtection descriptor as described in ISO...
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8.5 MPEG Common Encryption
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8.5.0 Protection System Specific Header
Players shall be able to process 'pssh' boxes from both the Initialization Segment and from Media Segments. Players may ignore 'pssh' boxes for protection systems that they do not understand. The initialization segment and/or media segments may carry 'pssh' boxes. For each DRM SystemID, if DRM specific data is present ...
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8.5.1 Key Rotation
For content using key rotation and conforming to this profile, the KID within an AdaptationSet shall not change more frequently than every 120 seconds.
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8.5.2 Random access requirement
Content shall be encrypted such that it can still satisfy the requirement for a type 1 or type 2 SAP as defined by MPEG DASH. This means that a Player having a suitable licence shall be able to decrypt any Media Segment using only information carried in that Media Segment plus information from the Initialization Segmen...
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8.6 Encryption Mode
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8.6.0 Encryption Usage
Media data shall be encrypted using AES 128-bit in CTR or CBC mode using the 'cenc' or 'cbcs' scheme as defined in ISO/IEC 23001-7 [7], clause 9. AdaptationSets using the 'cbcs' scheme shall not be labelled with the 2014 DVB DASH profile URN urn:dvb:dash:profile:dvb-dash:2014. Presentations that include one or more Ada...
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8.6.1 Constraints on the SampleAuxiliaryInformationOffsetsBox
In order to ensure that the Player has access to the sample auxiliary information before it is needed to decrypt a sample, the offsets in any 'saio' box shall reference data that is stored after the start of, and before the end of, the 'moof' box that contains the 'traf' box that contains this 'saio' box. As a means of...
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8.7 Mixing Non-Encrypted and Encrypted Content/Information
An MPD including encrypted video and/or audio may include information that is not encrypted such as subtitles (see clause 7 of the present document) and events (see clause 9 of the present document). Where events are carried in-band in a video or audio stream using the 'emsg' box, common encryption does not support enc...
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9 Carriage of Generic Streams and Events in DASH
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9.1 Events
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9.1.1 Background (informative)
MPEG DASH defines a generic event mechanism that supports two delivery methods. Events can be signalled in the MPD, or they can be carried in band within Media Segments. The semantics of the event are the same in each case. Inband events might be used where the event is closely related to the A/V content and is known p...
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9.1.2 Content programme metadata
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9.1.2.1 Definition
A DASH presentation may consist of one or more consecutive programmes, each of which has its own metadata. Content programme metadata may be delivered in the MPD by using an EventStream or in Media Segments using an InbandEventStream. It provides content identifiers and basic metadata relating to the current programme....
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9.1.2.2 Event message syntax
The format of the event payload carrying content programme metadata shall be one or more TV-Anytime BroadcastEvent elements that, when placed within the ProgramLocationTable element of the Default TVAMain fragment defined in Table 24, form a valid TVAnytime XML document. Table 24: Default TVAMain fragment <TVAMain xmln...
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9.1.2.3 Parental rating
Content programme metadata may include a parental rating in the BroadcastEvent/InstanceDescription/ ParentalGuidance element. A parental rating delivered in this way shall be considered to take precedence over any parental rating of the same classification scheme that is defined in the MPD using the AdaptationSet/Ratin...
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9.1.2.4 Example
<?xml version="1.0" encoding="UTF-8"?> <MPD xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="urn:mpeg:dash:schema:mpd:2011" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" ... etc ...> <BaseURL>http://cdn1.example.com/</BaseURL> <BaseURL>http://cdn2.example.com/</BaseURL> <Period id="1"> <Ev...
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9.1.3 Application messages
An application message is some information that is intended to be consumed by a higher level application and which relates to a particular time (and optional duration) on the media timeline. These can be considered similar to Stream Events as defined in ETSI ES 202 184 [16] and used in MHEG, MHP and HbbTV application e...
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9.1.4 Events for the Player
If the MPD@type attribute is set to 'dynamic' and the MPD contains a @minimumUpdatePeriod attribute, then this permits the server to update the MPD. Detailed MPD update procedures are provided in ISO/IEC 23009-1 [1], clause 5.4. However, if the minimum update period is used alone, there is a conflict between wanting cl...
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9.1.5 Long duration inband events
An inband event may have a duration that extends beyond the end of the media segment in which it is first delivered. In such cases, the content provider may choose to deliver the event only once, in which case a Player joining the stream at a later segment, or performing random access, will miss the event. Alternativel...
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9.1.6 Monitoring of InbandEventStreams
Players shall support monitoring of InbandEventStreams in all Representations that it is decoding at the time. Players shall not download a Representation solely to gain access to an InbandEventStream contained within it. InbandEventStreams with the same @schemeIdUri and @value attributes that are present in multiple A...
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9.1.7.1 Introduction
The "Hybrid Digital Radio (DAB, DRM, RadioDNS); SlideShow; User Application Specification" ETSI TS 101 499 [32] specifies mechanisms for providing live text messages and slideshows to internet radio devices. These consist of low update rate short text messages or image URLs which are loosely synchronized with the media...
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9.1.7.2 Use in preference to out of band data
Where one or more of the event schemes described in this clause are signalled as Inband Event Streams in an MPD, an application shall not connect separately to a different data source to get the same information (that is the inband events are to be used in preference) to avoid placing a load on systems in place to supp...
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9.1.7.3 Text messages
This event scheme is indicated by the following: schemeIdUri="urn:dvb:dash:radiovis:2016", value="1". The payload of this inband event carries a UTF-8 encoded string containing up to 128 characters. There is no termination character - the string is the length of the payload. This payload is a message to be displayed to...
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9.1.7.4 Simple slideshow messages
This event scheme is indicated by the following: schemeIdUri="urn:dvb:dash:radiovis:2016", value="2". The payload of this inband event carries a UTF-8 encoded string, containing up to 512 characters. There is no termination character - the string is the length of the payload. This payload gives the URL from which a sli...
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9.1.7.5 Enhanced slideshow messages
This event scheme is indicated by the following: schemeIdUri="urn:dvb:dash:radiovis:2016", value="3". The payload of this inband event is a UTF-8 encoded json message as defined in clause 7.4.3 of ETSI TS 101 499 [32]. All timing information for these events is carried in the json payload. The presentation time of the ...
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9.1.8 Integration of DVB-DASH and DVB Application Signalling
Application signalling is intended for use when the DASH stream represents a broadcast service and where it is necessary to bind an Application to one or more such services as defined in clause 4.2.1 of ETSI TS 102 809 [31]. Information about Applications associated with portions of the media timeline can be signalled ...
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10 Player Behaviour
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10.0 Introduction
This clause contains normative and informative text on client behaviour, however the normative aspects of client codec specific behaviour are dealt with in clause 5 (video), clause 6 (audio) and clause 7 (subtitles). Clauses 4, 8 and 9 also contain some client requirements.
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10.1 DVB Profile Support
Players shall support the 2014 DVB profile MPEG DASH as defined in the present document and indicated by "urn:dvb:dash:profile:dvb-dash:2014". All of the mandatory requirements and restrictions for that profile shall apply. Players may support the 2017 DVB profile of MPEG DASH as defined in the present document and ind...
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10.2 ISO BMFF Player Constraints
Following are constraints on the Player with respect to ISO BMFF format: • Players shall support the usage of the track fragment run box ('trun') with negative composition offsets in order to maintain audio visual presentation synchronization. NOTE: Negative composition offsets were added to ISO/IEC 14496-12 in Amendme...
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10.3 Bitstreams, Luminance Resolutions and Frame Rates
Players supporting H.264/AVC shall support at least one of the AVC player conformance points defined in ETSI TS 101 154 [3], clause L.2. Players supporting HEVC shall support at least one of the HEVC player conformance points defined in ETSI TS 101 154 [3], clause L.2. A Player that supports HD content shall support th...
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10.5 Playback Across Periods
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10.5.1 Background
Content with multiple Periods may be created for different reasons, for example: • to enable splicing of content, for example for advert insertion; • to provide a synchronization point to avoid drift in segment numbering; • to remove or add Representations in an Adaptation Set; • to remove or add Adaptation Sets; • to ...
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10.5.2 Content Offering with Multiple Periods
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10.5.2.1 General
If content is offered with multiple Periods, then the content provider should offer the content such that the total media presentation time of a Representation is as close as possible to the actual Period duration. It is recommended that the Period duration is the maximum of the presentation durations of the Representa...
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10.5.2.2 Associated Adaptation Sets across Periods
The content provider may express that the media components contained in two Adaptation Sets in two different Periods are associated by assigning equivalent Asset Identifiers to both Periods and by identifying both Adaptation Sets with identical value for the attribute AdaptationSet@id. If Adaptation Sets in two differe...
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10.5.2.3 Period Continuity
Content providers may explicitly signal that Adaptation Sets across Periods are period-continuous. It may do this by providing the following signalling: • From the first Period: - PID means the Period@id attribute value. - AID means the value of the @id attribute of the Adaptation Set to be Period continuous. • In subs...
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10.5.3 Player Requirements and Recommendations
Typically, at a Period boundary no continuity in terms of content offering is ensured. The content may be offered with different codecs, colour primaries, transfer characteristics, language attributes, content protection and so on. The Player should play the content continuously across Periods, but there may be implica...
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10.6 Trick Mode Implementation (informative)
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10.6.0 Introduction to Trick Mode
The terms "trick mode" refers to playback in any mode other than forward playback at the recorded speed of the audio/video content ("1x"). Examples include fast forward, slow motion, reverse, and random access. Random access may involve skipping to a presentation time, a scene, or a chapter to begin playback, and a men...
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10.6.1 Player Enabled Trick Modes
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10.6.1.0 Introduction to Player Enabled Trick Modes
Trick mode playback is primarily implemented in players, and uses unspecified decoding and synchronization methods that sometimes require decoding partial bitstreams that violate H.264/AVC buffer and timing models. A player may pause or stop a Media Presentation. In this case the player simply stops requesting Media Se...
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10.6.1.1 Fast Forward H.264/AVC Long GOP fast decoding and frame dropping
Lower bitrate video Representations in an Adaptation Set are typically subsampled with fewer horizontal and vertical samples than the Adaptation Set's nominal display resolution, and can usually be decoded at a higher frame rate in a decoder that is initialized for a higher quality Representation. Output frames may be ...