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
00031001_01 00031001 Object Objects start 00:30 dur: 00:20 00031001 00000001 XML Representation Use new version of the EBUCore schema -20.05.01.0AC_00031001AT_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-30-25.05.01.0 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> -20.05.01.0-22.06.01.1-24.07.01.2 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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