Re: compressing compressed video

This one time, at band camp, James Kim wrote:

Chris Johnson wrote:

Not true.

The reason why DivX/XviD/MPEG/MP4, et al, (also JPEG) don't compress further using a standard archival package is not due to the lossly compression, but due to the final layer of lossless compression applied to the lossy data stream. The results from the lossy stage are typically quite compressible, so running something like LZH over the output before it's turned into a file is built into the standards. 

Not true is not true:

Your talking is purly based on implementational points of view. However, my previous explanation coresponds to theoretical principles. Regardless of its actual implemenation method, the principle of lossy compression, which has been illustrated in my previous thread, can not be changed.

-James (^o^)

Your "principle" of lossy compression compression is irrelevant. What's more, you're talking about implementation as much as I am. No lossy video compression system produces a perfectly compressed data stream in one black-box maneuver. You're mixing up file formats with individual processes. The initial lossy treatement of the video stream always results in a data stream that benefits from lossless compression, but has very little time to do it.

As such, a compression program that can roll back any lossless stages and take as long as it needs to efficiently pack the lossy data is able to compress an existing video file quite considerably, without any loss in quality. The cost is that a time consuming process it required at the other end while a valid video file is recreated before it can be watched.

As such, if there was a video file format that didn't implement any lossless compression after the lossy stage was completed, the playable files would be larger than existing files, but they would compress into (PAQ/RAR/7z) archives much smaller than anything typically being distributed today.

If either a "recompresser" for video files, or a "lossy uncompressed" video format is created, video files currently being distributed around the 'Net could experience a significant reduction in size.
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