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Audio Definition Model for Flexible File Formats Dave Marston BBC R&D.

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Presentation on theme: "Audio Definition Model for Flexible File Formats Dave Marston BBC R&D."— Presentation transcript:

1 Audio Definition Model for Flexible File Formats Dave Marston BBC R&D

2 Involvement ● EBU Groups: ● FAR-BWF (BWF file, audio expertise) ● MIM-MM (EBU Core, metadata expertise)

3 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.

4 Future Multichannel Audio ● Channel based ● e.g. stereo, 5.1, 22.2 ● Scene based ● e.g. Ambisonics ● Object based ● Audio objects with stationary or moving spatial properties. ● Combinations of all three

5 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!

6 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 A single sequence of audio samples. Block A division of a channel in time. Pack A set of audio channels that belong together. Object A pack with time limited properties. Type The type of audio channel, whether direct speakers, Ambisonic component, audio object, etc. Content Objects with the actual audio. Programme A set of content that derived from the same material.

7 Audio Definition Model Diagram audioStreamFormataudioTrackFormat audioPackFormataudioObject audioContentaudioProgramme audioChannelFormat audioBlockFormat 'chna' chunk Content Format Track No audioTrackUID audioTrackFormatIDRef audioPackFormatIDRef

8 Simple Channel Based Example Track PCM_FrontLeft 00010001_01 Stream PCM_FrontLeft 00010001 Pack 3.0 00010005 Channel FrontLeft 00010001 Block start N/A 00000001 Object 3.0 00011005 00000001 00000002 00000003 Track PCM_FrontRight 00010002_01 Stream PCM_FrontRight 00010002 Channel FrontRight 00010002 Block start N/A 00000001 Track PCM_Centre 00010003_01 Stream PCM_Centre 00010003 Channel Centre 00010003 Block start N/A 00000001 Track NoUIDTrackIDPackID 1 0000000100010001_0100010005 2 0000000200010002_0100010005 3 0000000300010003_0100010005

9 Coded Audio Example Track data1 00040001_01 Stream DolbyE_3.0 00040001 Pack 3.0 00010005 Channel FrontLeft 00010001 Block start N/A 00000001 Object 3.0 00011006 00000001 00000002 Track data2 00040001_02 Channel FrontRight 00010002 Block start N/A 00000001 Channel Centre 00010003 Block start N/A 00000001 Track NoUIDTrackIDPackID 1 0000000100040001_0100010005 2 0000000200040001_0200010005

10 Object Based Example Track PCM_Object1 00031001_01 Stream PCM_Object1 00031001 Pack Objects 00031001 Channel Object1 00031001 Block start 00:00 dur: 00:05 00000001 Object Objects start 00:30 dur: 00:20 00031001 00000001 Track NoUIDTrackIDPackID 1 0000000100031001_0100031001 Block start 00:05 dur: 00:08 00000002 Block start 00:13 dur: 00:07 00000003

11 XML Representation <audioChannelFormat audioChannelFormatID="AC_00031001" audioChannelFormatName="Object1" typeDefinition=”Objects”> -20.0 5.0 1.0 … … <audioStreamFormat audioStreamFormatID="AS_00031001" audioStreamFormatName="Object1" typeDefinition=”PCM”> AC_00031001 AT_00031001_01 <audioTrackFormat audioTrackFormatID=”AT_00031001_01" audioTrackFormatName="Object1" typeDefinition=”PCM”/> Use new version of the EBUCore schema

12 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

13 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. -20.0 5.0 1.0 -22.0 6.0 1.1 -24.0 7.0 1.2

14 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

15 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'

16 Standard XML Definitions Where does the XML go? bext chunk axml chunk data chunk fmt chunk chna chunk Custom XML Definitions Refers to 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.

17 'chna' chunk 1 00010005 00010001_01 00010002_01 00010003_01 TrackNo audioPackFormatID audioTrackFormatIDaudioTrackUID 2 00010005 3 Track 1 Track 2 Track 3 Simple 3.0 Channel Example First 4 digits specify type of stream. 0001 = PCM 00000001 00000002 00000003

18 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.

19 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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