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BBC R&D White Paper WHP138

An mpeg video editor using AAF
R. Storey

Keywords
AAF, MXF, Edit Protocol, long GoP mpeg, editing, logging, ingest

Abstract
This paper describes a part-completed piece of work that attempts to answer two key questions. The first is how to link production processes together? The second is, can a long GoP video compression format be usable for professional editing? The first of these questions is important for professional users since production tools are normally supplied by many vendors and should ideally be connectable without needing human intervention. The second question impacts storage costs. Large volumes of content require efficient compression to be affordable; this means temporal compression (long GoP) and variable bit-rate, no matter what compression format is used.

The method proposed for linking production processes is to use the AAF Edit Protocol¹. The AAF sdk provides software objects that embody a class structure capable of describing production metadata. The sdk is large and flexible so there are many places you could potentially place each piece of metadata. This means an application developer would need to anticipate each one in order to avoid data loss. The Edit Protocol avoids this complication by constraining each piece of production metadata to appear at a single specified place.

The long GoP editing question is answered using mpeg 2 compression. This format was chosen simply because it is relatively mature and there are efficient software development kits available. The principles could equally well be applied to more modern compression methods.

The Application, including its own DirectShow filters, is coded in Pascal using Borland Delphi. The Delphi component set and the editing application can be found on SourceForge².