Lossless vs. Lossy

[WillatSMU]

If you were streaming something real time which do you think would be faster?


Sending out a lossless compressed package...

OR

Decompressing the lossless compressed package then recompressing it as lossy?

ALSO

In this you can split the lossless compressed package in 2 so if it is faster to decompress then recompress would it be faster to...

split the lossless package then do to seperate recompressions

OR

split the lossy compressed package in 2 and send it out? (This way the quality is minimally degraded)


Thank you

[WillatSMU]

Does anyone have any idea or experience with this?

[Shelwien]

There's no specific answer, it depends on the circumstances.
If you have a slow network and lots of computing power, then recoding could be faster.

[WillatSMU]

Their would be a processor exclusively dedicated to altering the compressed packages but the network speed will vary greatly. Also they are in an MP4 format so I know that will play a large role in this, sorry for excluding this information.

[WillatSMU]

Or can you manipulate the original package without decompressing by dropping the pixel density which essentially turns it into lossy but saves the overhead of decompression? Would this be faster?

[Piotr Tarsa]

Ogg Vorbis provides bitrate peeling, but its results were very bad the time I checked.

JPEG2000 does hierarchical coding and "ordinary" JPEG has progressive mode (though software/hardware unable to decode progressive JPEGs is not rare) so dropping the bigger layers from hierarchy or late scans from progressive images would be roughly equal to dropping the pixel density.

I'm not an expert in lossy compression but I think there are at least few popular formats which support something like hierarchical coding, ie better approximations of source signal is obtained by decoding the worse approximation and then improving the result using additional data.

On the other hand, I haven't heard of anything serious and competitive that supports converting from lossless to lossy without decoding.

[Bulat Ziganshin]

afair, wavpack has lossless=lossy+correction mode

[jethro]

Yes, and there is LossyWav which also has possibility of creating correction file.