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Lossless and Lossy Editing Workflows - TreetWiki

Lossless and Lossy Editing Workflows

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(Created page with '== Lossless and Lossy Editing Workflows == In television and cinema, captured and edited footage is sacred and may go through many different processes before it reaches the inte...')
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== Lossless and Lossy Editing Workflows ==
 
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In television and cinema, captured and edited footage is sacred and may go through many different processes before it reaches the intended audience.  For example, captures may be assembled into scenes which are then later recombined by another editor.  Or, portions of films or movies may be produced by outside contractors.  Those parts are then combined to form the final edit.    Even final edits can then be reused.  For example, a motion picture edit may be recombined into a television edit, trailers may be created, or "Making Of" DVD extras may be created.
In television and cinema, captured and edited footage is sacred and may go through many different processes before it reaches the intended audience.  For example, captures may be assembled into scenes which are then later recombined by another editor.  Or, portions of films or movies may be produced by outside contractors.  Those parts are then combined to form the final edit.    Even final edits can then be reused.  For example, a motion picture edit may be recombined into a television edit, trailers may be created, or "Making Of" DVD extras may be created.
Lossy workflows result when input material is re-encoded by an editing package during editing, and possibly re-encoded again when the final export of video.  Most prosumer editing packages such as iMovie or Windows Movie Maker do this by default to make life simple and easy.  In addition, most consumers who do editing are not concerned with absolute quality standards and will never be submitting videos for broadcast or inclusion in HD studio productions.  Most likely, consumer video will be presente on the web using sites like YouTube where lossy re-encoding is normal and quality standards are low.
Lossy workflows result when input material is re-encoded by an editing package during editing, and possibly re-encoded again when the final export of video.  Most prosumer editing packages such as iMovie or Windows Movie Maker do this by default to make life simple and easy.  In addition, most consumers who do editing are not concerned with absolute quality standards and will never be submitting videos for broadcast or inclusion in HD studio productions.  Most likely, consumer video will be presente on the web using sites like YouTube where lossy re-encoding is normal and quality standards are low.
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Lossy workflows result because the editing package has no choice except to convert video from the timeline into some intermediate editing format, then to convert again when the final project is saved.  While it may ''appear'' that frames are being transferred unchanged, and even close inspection may appear to reveal no differences, there are subtle differences in edges and "color fields" which gradually will degrade video edited using lossy workflows.
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The reason why conversion must be performed is not always obvious.  Here are some of the important reasons:
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* Codecs which are convenient for internet transfer are not designed for editing purposes.  Editors require good [[Intermediate Codecs]] in order to assure rapid editing.  So, the format of codecs such as H.264 and Mpeg2 do not allow exact frame extraction and frames ''must'' be constructed and converted because of the very design of these codecs.
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* Non-intermediate codecs use IBP groups to store picture data.  So, a second of video may contain only one actual frame of video (called an I-Frame) followed by algorithmic frames (P and B) which instruct the codec how to assemble the full frame.  When clips are dropped onto timelines, these frames do not align, and thus the editing package must decompress the IBP groups so that all the frames are stored as a full-frame internal graphic.  Intermediate codecs are designed so that they do not have this limitation and each frame can be transferred in its exact form.
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The figure below shows a lossy workflow.  Note the following:
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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.
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* 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.

Revision as of 14:32, 15 July 2011

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