mxf & aaf

16/10/08

Matthias De Geyter

MXF & AAFMXF & AAF

VRT-medialab: onderzoek en innovatie2

Outline

Introduction

! Why Do We Need Them?

What Are They?

Some Concepts

! The Source Reference Chain

! Operational Patterns

A Few Practical Examples

! Workflows & Issues

A Key to Success: Application Specifications

What the Future Brings

! HD

! Increased Functionality (& Complexity)


Introduction


Introduction

Why Do We Need Them?

! To realize this content-central workflow model, a file format isneeded that satisfies some requirements

– Able to carry metadata, video and audio

– Possible to work on the file before transfer is complete

– Random access to material (partial file transfers)

– Open, standardized, compression-independent

– ...

! To meet these requirements MXF (the Material ExchangeFormat) was developed

– Work by the Pro-MPEG Forum and the AAF Association(now AMWA), taken to SMPTE for standardization

– The AAF Association was working on a file format for postproduction: the Advanced Authoring Format

– MXF & AAF are interoperable, share data model

– Zero Divergence Doctrine (ZDD)


:

a wrapper format intended for the interchange offinished and almost finished audiovisual material andassociated metada

Defines the actual, physical file format

:

a wrapper of metadata and essence designed for postproduction interchange

Clear distinction between Object Model and StorageLayer

More complex

What Are They?

next slides


What Are They?

Structure of an MXF file

! Partitions

– logically divide the file in manageable parts (e.g. for errorrecovery)

– 1 header partition, 0 or more body partitions, 0 or 1 footerpartition

! Index Table

– lookup table which converts a desired time offset on thetimeline to a byte offset within the file

! Header metadata: structural and descriptive metadata

– Structural metadata includes source reference chain


What Are They?

Every property, set of properties, chunk of essence in an MXF file is

wrapped in a KLV triplet

! Key is 16-byte number that uniquely identifies content of triplet

! MXF Parser can skip value bytes when key is not recognized(SMPTE RP210) by means of length

! Unknown keys: dark

Essence container divided into content packages of approximately

equal duration

! Different essence categories

– System item (metadata)

– Picture item

– Sound item

– Data item (continuous data, no picture)

– Compound item (intrinsically interleaved; e.g. DV essence)


What Are They?


A super edit decision list (EDL)

! To describe a composition on the timeline (including effects)

! Can also include essence

! More complex than MXF (effects, multi-camera)

! Does not meet all MXF requirements (process file duringtransfer)

Supported by various vendors: Avid, Sony, Adobe, ...

! AAF Edit Protocol to standardize effects + restrictions

Apple (Final Cut Pro) uses its own EDL format (XML)

! Conversion is possible (Automatic Duck)

Freely available SDK

! Store files as Structured Storage, KLV and XML

What Are They?


A super edit decision list (EDL)

What Are They?


Some Concepts

The Source Reference Chain: MXF and AAF share the

same data model. Material Package

Sequence (defines track duration)

SourceClip

SourceClip

SourceClip

Track (defines track origin)

Top-Level

File Package Sequence (defines track duration)

SourceClip SourceClip

SourceClip

Track (defines track origin)

SourcePackageID and SourceTrackID of the

File Package segment define respectively

the Source Package and the Track containing the derivation of the essence.

This provides historical annotation.

Source Package

Sequence (defines duration)

Track (defines origin)

Essence Container

Essence Descriptor e.g. Tape Descriptor

Essence Descriptor e.g. MPEG

SourcePackageID and SourceTrackID of the Material Package segment define

respectively the File Package and the Track containing the essence.

SourceClip

Start Position SourceClip

Duration

SourceClip Start Position SourceClip

Duration

Output timeline

Stored Essence

History

1)For MXF

•Packages are

identified by a

UMID (unique

identifier)

•The UMID is used

as a reference

mechanism


...

Some Concepts

The Source Reference Chain: MXF and AAF share the

same data model. 2)For AAF

•Same concepts, different names

•Material Package ! MasterMob

•Source Package ↔ SourceMob

•Timeline Track ↔ TimelineMobSlot

•Introduces CompositionMob

•Creative decisions on how to

combine/modify essence

Reference by UMID

Deeper source packages/mobs can be used

for media tracking

•Quality preservation (limit #generations)

•Rights managements


Some Concepts

Operational Patterns

Tape equiv.

Multitrack

Multilingual

DVD

Playlist EDL

•Control the

complexity of the

source reference

chain " control

complexity of MXF

en/decoder

•Constraints on the

file

Specialized pattern:

OP-Atom (mono-

essence)

Possible to use

for repurposing



File-based camera

MXF OP-Atom

Central Storage

MAM system

Avid Editor

Apple editor

Play out

server

MXF OP-Atom

MXF OP-1A

MXF OP-1A

QuickTime

Rewrapping needed

Rewrapping needed

•Rewrapping or

•QT reference to MXF

•MXF4Mac plugin



File-based camera

Central Storage

MAM system

Avid Editor

Apple editor

Play out

server

MXF OP-Atom

MXF OP-1A

MXF OP-1A

QuickTime

Rewrapping needed

•Rewrapping or

•QT reference to MXF

•MXF4Mac plugin

MXF OP-1A

Rewrapping needed



File-based camera

Central Storage

MAM system

Avid Editor

Apple editor

Play out

server

MXF OP-Atom

MXF OP-1A

MXF OP-1A

QuickTimeMXF OP-1A

Browse editing on lowres



Multi-camera production


Next to rewrappings (specialized companies: MOG

Solutions, OpenCube), the breadth of the standard can

cause interoperability problems, even within an OP

! E.g. timecode: which timecode? (EBU Recommendartion R122)

! Which audio in MXF wrapped DV?

Keep it simple!

Enter the Application Specification!

Revision of MXF standard (SMPTE 377M)



A Key to Success: ApplicationSpecifications

Constrain the number of options associated with the use

of MXF in a facility

Document the operational practice

Restrictions dependent on the problem space /

application:

! E.g. DV25 for news, IMX50 for general purpose programs

! Play-out automation environments: correct time code(subtitles) and aspect ratio very important

! Archival (long-term) preservation: less tolerant regardingstandard compliance

! ...


A Key to Success: ApplicationSpecifications

Example:

! Essence is 25Mbps IEC-DV

! OP is OP-1A

! Audio within Compound Elements is not used

! A System Item is present (with accurate time code in UserTime)

! Material Package contains 1 timeline track, 1 video track and 2or 4 audio tracks

! ...

Important to prevent and solve interoperability problems

! In quality control of existing files (later)

! As specifications for vendors



New challenges arise while the basic implementationsare becoming mature

! Advent of HDTV

– Impact on bandwidth & storage requirements...

– ...Impact on compression formats (video codecs)...

– ...but also on MXF

! Increasing demand for repurposing

– Proliferation of devices

– Value-added content on digital television

! Growing importance of workflow automation

– Basic functionality is there, let’s improve efficiency

– Service oriented architecture: services & humaninteraction

•Higher Operational Patterns

•Metadata e.g. about Region

of Interest (ROI)

•Media Tracking (source

reference chain)

•Metadata (e.g. Quality

Control)



HD support of MXF: evolution similar to SD??

! Again: start simple & extend functionality because of...

– Introduction of new video codecs

– Multi-channel audio: work within SMPTE

– Identification and labeling of individual audio channels (forrouting)

– Mapping multi-channel audio metadata in MXF

– ...

– Time labeling

– Next to the different implementations...

– ...problem with higher frame rates (>39)

– Not all codecs support this: time code implementationdependent on compression format

– Revision of SMPTE 12M (12M-1, 12M-2); workaround

– EBU Recommendation (R122) needs update



Metadata in MXF (not HD-specific)

! Less flexible than MAM system and its database

! Useful for e.g.

– Archival purpose

– Tightly coupled essence–metadata quite stable over time

– Subtitles, region of interest (ROI) information

– MXF validation reports

! Adding or removing metadata should happen in a flexible way

– Revision of SMPTE 377M includes appropriatemechanism (application metadata plugin)

Higher operational patterns and media tracking

! Discussed earlier

! Application Specifications needed (AMWA; http://amwa.tv)

mxf & aaf

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