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Lossless and Lossy Editing Workflows - TreetWiki

Lossless and Lossy Editing Workflows

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* Input clips have IBP groups which do not align with the I-only frames of the intermediate codec and don't align with the IBP frames of the final exported video.  
* Input clips have IBP groups which do not align with the I-only frames of the intermediate codec and don't align with the IBP frames of the final exported video.  
* In the example, two conversions are done.  One conversion to decompress the video on the timeline, and another conversion when the intermediate edit is exported to final video.  This is typical.
* In the example, two conversions are done.  One conversion to decompress the video on the timeline, and another conversion when the intermediate edit is exported to final video.  This is typical.
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[[File:Lossy Workflow.png]]
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=== Lossless Workflow ===
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By contrast, lossless workflow preserves every frame of video exactly.  In a good studio workflow, the video frames captured by cameras move through the system unmodified and are pixel-for-pixel identical through even hundreds of generations of editing and re-use.  By contrast, a lossy workflow can only withstand two or three editing re-use sessions at best before visible artifacts and color shifts begin to appear in results.
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In a lossless workflow, studios observe the following rules:
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* A single format is chosen for production work and it is used throughout the editing, capture, and storage process.  Codecs used for this purpose are almost always specially designed [[Intermediate Codecs]].
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* When video is provided by another source, it is always re-encoded immediately into the chosen format used by the studio.  Therefore, the video will mix and match easily with existing footage, and archives and re-edits work normally.
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The figure below shows a lossless workflow.  Note the following:
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* Because there are no IBP groups present in clips on the timeline, each frame is independent and can be moved into the intermediate edit unchanged.
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* Professional editing systems are designed to recognise that clip format and intermediate format are identical.  In such cases, they do not even store intermediate frames at all, but display information directly from the timeline.  This results in almost instantaneous editing, scrubbing, and rendering.
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* Because the final export format is the same as the clip and intermediate format, the final frames match pixel-for-pixel with the frames present on the original timelines.
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* Avid and Final Cut systems have the ability to output what are called "reference movies" which actually refer to the exact clips on the timeline rather than copying the frames at all.  Thus, an long and complex edit involving terabytes of content may result in finished files which are only a fraction of the original size.

Revision as of 14:41, 15 July 2011

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