Audio Definition Model for Flexible File Formats Dave

Audio Definition Model for Flexible File Formats Dave

Audio Definition Model for Flexible File Formats Dave Marston BBC R&D Involvement EBU Groups: FAR-BWF (BWF file, audio expertise) MIM-MM (EBU Core, metadata expertise) What is the Audio Definition Model? Formalised way of describing audio for file formats. Initial file format will be Broadcast WAV (BWAV). Specified by EBUCore XML schema.

Model can be used more generally. Aim to make it the primary description model for as many formats as possible. Future Multichannel Audio Channel based Scene based e.g. Ambisonics Object based e.g. stereo, 5.1, 22.2 Audio objects with stationary or moving spatial

properties. Combinations of all three Cooking with Audio! Audio Definition Model is like a shopping list of ingredients. Each ingredient has a formal description. BWAV file is like a shopping bag containing the actual ingredients. BWAV 'chna' chunk is like the bar-codes on each item. The ADM is NOT the recipe though! Terminology Track A single set of samples or data in the storage medium. Stream

A combination of tracks (or one track) required to represent a channel, an object, or a group. Channel Block Pack Object Type A single sequence of audio samples. Content Programme Objects with the actual audio. A division of a channel in time. A set of audio channels that belong together. A pack with time limited properties. The type of audio channel, whether direct speakers, Ambisonic component, audio object, etc. A set of content that derived from the same material. Audio Definition Model Diagram audioProgramme audioContent audioObject

'chna' chunk Content Track No Format audioPackFormat audioTrackUID audioTrackFormatIDRef audioPackFormatIDRef audioStreamFormat audioChannelFormat audioBlockFormat audioTrackFormat Simple Channel Based Example PCM_FrontLeft Channel FrontLeft Block start N/A 00010001 00010001

00000001 Track Stream PCM_FrontRight PCM_FrontRight Channel FrontRight Block start N/A Pack 3.0 00010002_01 00010002 00010002 00000001 00010005 Track PCM_Centre

Stream PCM_Centre Channel Centre Block start N/A 00010003_01 00010003 00010003 00000001 Track Stream PCM_FrontLeft 00010001_01 Object 3.0 Track No UID TrackID

PackID 00011005 1 00000001 00010001_01 00010005 2 00000002 00010002_01 00010005 00000001 00000002 00000003 3 00000003 00010003_01 00010005

Coded Audio Example Track data1 Stream DolbyE_3.0 00040001_01 00040001 Track data2 00040001_02 Channel FrontLeft Block start N/A 00010001 00000001 Channel FrontRight Block start N/A

Pack 3.0 00010002 00000001 00010005 Channel Centre Block start N/A 00010003 00000001 Object 3.0 Track No UID TrackID PackID 00011006 1

00000001 00040001_01 00010005 2 00000002 00040001_02 00010005 00000001 00000002 Object Based Example Track Stream PCM_Object1 00031001_01 PCM_Object1 Channel Object1 00031001

00031001 Block start 00:00 dur: 00:05 00000001 Block start 00:05 dur: 00:08 00000002 Pack Objects 00031001 Block start 00:13 dur: 00:07 00000003 Track No 1 UID TrackID PackID 00000001

00031001_01 00031001 Object Objects start 00:30 dur: 00:20 00031001 00000001 XML Representation Use new version of the EBUCore schema -20.0 5.0 1.0 AC_00031001 AT_00031001_01

Standard Configuration File Many configurations will use common channel types (e.g. stereo, 5.1, 22.2, Ambisonics). Therefore use an external standard reference XML file. M-30 -25.0 5.0 1.0 Custom Configuration For non-standard channel definitions, particularly audio objects, a custom configuration file must file generated. This is what is carried in the 'axml' chunk.

typeDefinition=Objects> -20.0 5.0 1.0 -22.0 6.0 1.1 -24.0 7.0 1.2 What are BWAV and RF64 Files? WAV is a RIFF file for audio BWAV = Broadcast WAV BWF = Broadcast WAV File RF64 = WAV file for >4GB size files BWAV have a 'bext' chunk MBWF is a RF64 file with a 'bext' chunk Chunks Resource Interchange File Format (RIFF)

Data stored in chunks header, length & data. WAV chunks: 'RIFF' : tells you its a WAVE file 'fmt ' : contains sample-rate, number of channels, etc. 'data' : contains audio samples. BWAV chunks: 'bext', 'axml', 'link', 'levl', 'mext', 'qlty', 'dbmd' Where does the XML go? fmt chunk bext chunk Refers to

chna chunk Standard XML Definitions Refers to data chunk Custom XML Definitions axml chunk is stored in If no custom XML definitions are used, then no axml chunk is required. Standard XML definitions do not need to be included in the file. 'chna' chunk Simple 3.0 Channel Example Track 1 Track 2 Track 3 TrackNo

audioTrackUID audioTrackFormatID audioPackFormatID 1 2 3 00000001 00000002 00000003 00010001_01 00010002_01 00010003_01 00010005 00010005 00010005 First 4 digits specify type of stream. 0001 = PCM Current Status

EBU Tech 3364 Audio Definition Model now published. EBU Core v1.5 (EBU Tech 3293) schema containing ADM soon to be released. ITU Contributions being made. Future Work A list of standard configurations will be drawn together. Database Reference XML file Audio Object parameters need continual refinement. Libraries/APIs for parsing and generating ADM metadata to be developed. Look at streaming methods.

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