Many lossless audio codec comparisons look at only compression ratio and encoding speed. FLAC decoding is the fastest among lossless codecs and its compression is within 3% of even the most complex codecs. Note that the compression ratios of all lossless codecs falls in a quite narrow range; the difference between the very best and very worst is only around 7%, and only 4% for the practical codecs.
The evaluation of lossless codecs typically depends mainly on features other than speed and compression, which is what our first table shows: features like how well it is supported in devices and software, licensing, etc. For more information on this matter, take a look at the comparison at Hydrogenaudio. Additionally, as archiving is one of the main applications for a lossless codec, of chief importance is the ability to use and recover data in the future. FLAC stands out as the most widely supported codec, and the only codec that at once is non-proprietary, is unencumbered by patents, has an open-source reference implementation, has a well documented format and API, and has several other independent implementations.
*At the time of writing, which is 6 jan 2013
The machine used for running the test has an Intel Core2Duo T9600 with 4GB of RAM and is using Kubuntu 12.10. The tests are run from ramdisk, as the harddisk is a bottleneck in certain cases. For the codecs that only have Windows-support, the binaries are used through WINE. Measured is the so called cpu time used, not the real time used, except for WMA Lossless and Real Audio Lossless which were timed by hand.
The audio corpus currently consists entirely of CD albums. These are 29 CDs whose genres range from rock to pop to metal to classical to world. The following graphs display the results of these tests: the compression ratio as a function of encoding and decoding speed for the currently most used lossless codecs for all their recommended compression modes.
In the graphs below you can see both the compression and decompression performance of all tested codecs by their speed relative to 'playing speed' on the x-axis and their compression relative to WAVE on the y-axis. The connected dots for each codec are its different presets. For more information on the test environment, codecs and settings, please see the exhaustive report here (PDF).
Please keep in mind that the differences considering archieved compression are exaggerated: in fact, the difference between the best and worst compression is a factor 1000 in time, but only about 7% in space used. So, please mind the axes.
The CD's used in this test are listed below, with a very general indication of the kind of music it should represent.