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Codec Efficiency Comparison Test (iPod)

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senab:
Intro

Being a bit bored today, I thought i'd do a bit of a comparison test of how efficient they are when given files with varying bitrates. I used most of the codec's supported by Rockbox, but left some out (WAV - obvious, AC/3 - fairly useless at low bitrates). And not to mention these results are only really useful for iPod's and other PortalPlayer based builds.

Method

To do this test I compiled a new 5G iPod Video build from cvs, but edited the debug_menu.c file to not display the buffer progress bars in the 'View Audio Thread' screen. This was because the progress bars would use extra cpu cycles to render, and I wanted make the cpu to be doing as much audio decoding as possible.

I then picked a track off a cd, and start encoding it with various encoders and settings (which can be seen in the table below). For a more detailed look at the files, this analysis was done here.

I then loaded my iPod with my new Rockbox build and the files in a folder. When booting Rockbox I cleared my settings, thus making sure no DSP or equalizer was on. I also changed the WPS to one without a peakmeter (boxes_320x240).

I then played back each file one by one, leaving it on the WPS screen until around 50% of the track was played. I decided to wait to 50% because by then, the audio would be filled and the boost ratio would have levelled out. I then went into the Debug menu --> View Audio Thread, and waited for the boost ratio to become level before recording the value.

Results

See here

Conclusion

After the recent optimizations to libFaad, AAC is decoding very nicely in realtime now. MP3 & Vorbis are decoding in very similar speeds across the bitrates, Vorbis has quality gains in lower bitrates though. Musepack was the most efficient lossy codec on test. I was quite suprised by just how well FLAC decoded even using q8 which is the highest compression level using libFLAC.


I'm not sure whether this test was anything good or worthwhile, but it may give you an indication of how efficient the codec's you're using are. Now of course, this test was done with a build not using any DSP's or fancy graphics, therefore if you're using these don't expect anything as low.

bk:
I'm assuming by "iTunes" and "Nero" you mean LC-AAC, right? I don't use Nero but I read somewhere that at low bitrates it will encode in HE-AAC.

Interesting results. I would have expected libmad (MP3) to be the fastest.

senab:
Yes LC-AAC. I put both Nero and iTunes in because Nero use's is "true" VBR, whereas iTunes' implementation of VBR is ABR, I just wanted to see if it makes any difference.  ;)

Davide-NYC:
Here's a stupid WPS that may be helpful: It has no alternating sub-lines, no peakmeter, no progressbar, no statusbar, etc.

I does give you the essential information you need for testing: playlist length and current position, filetype, bitrate, VBR/CBR, etc.

Let me know if this is at all useful.  ;D

[attachment deleted by admin, too old]

Rincewind:

--- Quote from: Davide-NYC on October 01, 2006, 03:41:46 PM ---Let me know if this is at all useful.  ;D

--- End quote ---

No it's not  ;D
(but it might be useful for other people)

When I "test" performance I usually leave the settings just the way I am normally using rockbox, "No side-effects" is an utopia anyway  :-\

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