Audio channel mapping and shuffling

[samdbmg]

Context
In the course of considering #188 one of the use cases discussed was describing audio channels: for example how to indicate a particular Flow was the left or right channel of a stereo pair. The ability to map Flows from the essence of others and generally use container_mapping also suggests space for a more complete way to map and shuffle audio channels in TAMS.

Description
Consider how the channel mapping or allocation in audio should be represented in TAMS, and more generally to what extent channels can be re-arranged by operating the Source/Flow model.

Consider for example whether two mono-essence single-channel audio Flows can be collected to form a stereo pair. How should a client identify which is Left and which is Right?

    block-beta
    columns 4

    a_f_a1["Flow A1 \n Audio \n container: audio/mp2t \n Audio 1"]
    a_ci_a1>"Collection Item \n Track: 1"]
    space:5
    a_f_s-- "collects" -->a_ci_a1
    a_ci_a1---a_f_a1

    a_f_s["Flow S \n Audio \n container: null \n Stereo Audio"]

    a_f_a2["Flow A2 \n Audio \n container: audio/mp2t \n Audio 2"]
    a_ci_a2>"Collection Item \n Track: 2"]
    a_f_s-- "collects" -->a_ci_a2
    a_ci_a2---a_f_a2

    classDef flow fill:#0092E1,color:#FFF
    classDef collectionItem fill:#C8ADC0,color:#FFF

    class a_f_s,a_f_a1,a_f_a2 flow
    class a_ci_a1,a_ci_a2 collectionItem

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Consider how this changes as different forms of capture take place: e.g. what happens with an input Flow that is all 16 channes of SDI audio in a single multiplex: how can stereo pairs be extracted then?

Use Case

• Representing the breadth of audio channel formats precisely, without relying on conventions that only apply in some circumstances
• Flexibility to re-arrange channels of audio without (necessarily) duplicating the underlying essence/samples, e.g. to pull out an alternative audio feed and present it as a primary in a separate Flow collection

[samdbmg]

Some initial notes in https://github.com/bbc/tams/tree/sammg/adr/audio-channel-mapping