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SMPTE / st2067-40

SMPTE ST 2067-40
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Consider adding support for DCinema Immersive Audio #22

Open dtatut opened 3 years ago

dtatut commented 3 years ago

Background

DCinema and IMF are both capable of transporting immersive audio bitstreams but with different constraints. Among them here are the main ones

  1. IMF strictly carries uncompressed PCM audio samples, while DCinema strictly carries DLC encoded audio samples
  2. IMF uses a different MXF operational pattern than DCinema (Op1a vs OpAtom respectively)
  3. IMF uses a different wrapping method than DCinema (clip-wrapped vs frame wrapped respectively)

While DCinema immersive audio could in theory be derived from IMF immersive audio, in practice several factors prevent this process from being efficient or even desired:

  1. DCinema immersive audio uses specific audio mixing conditions targeting cinema screening rooms.
  2. DCinema immersive audio authoring tools are wide-spread and produce directly ready-to-use files that can be incorporated into DCinema packages.

The factors listed above imply that DCinema workflows, that have been well-established for a decade now, are going to continue the production of immersive audio track files that differ from IMF immersive audio track files, both in nature and purpose.

IMF App #4 aims at being the vessel of choice for DCinema-oriented content mastering and preservation. Therefore it is important to consider the carriage of DCinema essence in its native form.

Proposal

IMF App #4 should define the following new entities in order to allow proper mastering and preservation of DCinema-oriented content, in the same spirit as colorimetry and timed text:

  1. add a new dedicated virtual track definition (e.g. DCDMImmersiveAudioSequence)
  2. define a new MXF mapping for ST 2098-2 that combines the bitstream restrictions and wrapping method of ST 429-18, but uses the operational pattern and container constraints defined in ST 2067-5

This approach would have several advantages:

  1. DCinema-oriented content can be carried into IMF App #4 in its most native form and wrapping method
  2. No further conversion/transcoding is required which eliminates extra human-driven QC tests
hnlocher commented 3 years ago

2021-03-01 35PM50 : The document will be carried to PCD3 as present, without this issue beeing resolved. Need to be tracked for future revisions.

dtatut commented 2 years ago

@hnlocher : I'm not sure why this issue has the tag "wontfix" and "next edition", it's confusing. A "wontfix" tag is normally used when the issue is not going to be fixed or addressed.