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Decoding performance on iPOD

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Buschel:
Hello everybody,

after using and playing around with rockbox I am now quite interested in the decoder performance of especially musepack on the PP-processor (iPOD). Did anyone made
measurements or profilings? Are there measurements which can be compared to e.g.
.mp2 or .mp3?
I just downloaded the source code and plan to get it compiled over the next weekend.
Of special interest is the synthesis filterbank which was quite well optimized for PCs
(586). I wonder if there is still some performance left to sqeeze out of the decoder on
the iPOD...

Anyone can give me some hints about current measurements (.mp2/.mp3/.mpc)?
Or any history on the optimizations made within the .mpc-decoder (I know there were lots of optimizations in 2005)?

thanks,
Buschel

stripwax:
Hi Buschel
Optimising decoder performance is definitely a hot topic, good to see you are interested in this!  Two good metrics for measuing "performance" are boost ratio, and battery life between charges (search the wiki for a good methodology for measuring battery life).  Boost ratio refers to the percentage of time that the CPU is running at a higher clock speed (as pp cpus have a variable frequency) - this is viewable in the rockbox debug menu.  Lowering the boost ratio should have the side effect of increasing the battery life between charges, of course.

Almost certainly ipod codecs can be optimised further - in fact rockbox devs will not formally 'release' the ipod rockbox port until battery life has improved considerably.  

You can also find some patches on the tracker relating to code optimisations for audio decoders, there may be some detailed profilings there too.

For example, here's some possibly relevant patches along this theme
http://www.rockbox.org/tracker/task/5226
http://www.rockbox.org/tracker/task/6705
http://www.rockbox.org/tracker/task/6848
http://www.rockbox.org/tracker/task/6734

Not sure anyone has conducted a thorough investigation of musepack performance compared to (say) tremor or mp3, would be interested in the results.

saratoga:
This week a plugin was added for benchmarking codecs that can give you the exact runtime, so no more need to use boost ratio.

Actually, if anyone is interested, it might be neat to make a wiki page like for the battery runtime ones, except for how fast each codec is on a given player with a given SVN revision.  

Llorean:
There would need to be a definition for proper testing: For example, always using the maximum bitrate the decoder allows, or do you use equal bitrates (128 for all lossy codecs, for example), or some standard bitrated decided in advance for each?

As well, at those bitrates, you should probably encode from the same .wav file just for consistency's sake.

saratoga:
Depending on the bandwidth to burn, maybe reference tracks in each format could be provided, that way the test is exactly the same for each person.  

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