The purpose of the comparison page is not only to show how compression ratios and encoding times using the flac reference encoder compare to other lossless encoders, but also to compare features (for example, some coders archive only and files must be uncompressed completely before playback can start). Keep a few things in mind:

• As far as I know, only two of the lossless encoders out there (flac and Kexis) are truly free (source code for Shorten is available but the license is more restrictive). Most others give out free binaries, but without access to the source, you are leaving your data to the whim of the maintainer for eternity; you have no way to port the program to another OS or fix it if it breaks. This can be a serious drawback unless the format has world-class clout (like MP3).
• The compression ratios and times are representative only of the reference encoder. They are not indicative of the limits of all FLAC encoders or the FLAC format itself since the format is open and extensible, and anyone is free to write a better FLAC encoder. And it is almost certain that the reference encoder itself will improve.
• Since FLAC supports streaming, it is at a slight disadvantage to the formats that don't because they don't have the extra overhead of all those frame headers.

I make an effort to keep this information as accurate as possible, but if any of the data is wrong, let me know and I'll correct it.

Reviewed encoders:

• flac of course.
• Kexis - An open-source source codec. Still in the alpha stage. No player or library support yet.
• LPAC - A closed source codec. At least it's available for more than just Windows, but there's only a Winamp plugin.
• Monkey's Audio - A closed source, Windows-only codec, with a Winamp plugin.
• Ogg Squish - An open source source codec that is no longer maintained. The version I tested, 0.98, was the latest I could find. I don't have Windows timing results but it is among the 'fast' coders, based on UNIX tests.
• Pegasus-SPS - A closed source, Windows-only codec.
• RKAU - A closed source, Windows-only codec.
• Shorten - A.J. Robinson's well-known codec; source is available here.
• WaveZIP - A closed source, Windows-only archiver. Uses the MUSICompress[tm] engine which supposedly has a patent. I used to have a link to the company that makes WaveZIP (GadgetLabs) but apparently they have gone out of business (maybe for trying to sell something that should cost nothing).
• WavPack - A closed source, Windows-only archiver.

Encoders I couldn't get a copy of:

• AudioPak
• WavARC

If you take maximum compression ratio and speed out of the picture (as you will see later, most coders exhibit similar performance), here is a subjective sort based on overall "usefulness". As far as features go, having source code gives you the most freedom since you can add anything you need that is missing; besides, open source projects tend to get better faster than closed source ones. A close second (depending on the user) would be OS support or plugin support.

The machine I used for encoding the test files is a PII-333 with 256 megs of RAM, running Windows NT 4.0 SP5. Unfortunately, Windows is the lowest-common-denominator platform for all the encoders.

The input corpus currently consists entirely of CD music tracks. In the future it may include more kinds of input (like speech, other sample rates/resolutions, etc). There are 14 tracks whose genres range from death metal to pop to classical to chant.

In all tables, the results are sorted by compression ratio, which is compressed size / uncompressed size. The first table is a summary of results on all input tracks. The remaining table shows the results of the encoders on each track.

Some interesting things to note: LPAC quality settings are not too stable with -r (which allows seeking during playback) turned on. In most cases the 'normal' mode makes the smallest file, and much faster. RKAU also has a tendency to get bigger in the 'high' mode. Shorten's method for quantizing the LPC coefficients is not very good which is the main reason why the fixed predictor runs are both smaller and faster.

Another ironic fact is that the encoders that are patented or cost money turn out to be the worst by most measures. SPS is so archane and crippled that I gave up trying to put together results for it after one track.

Codec Encode time Decode time Compressed size Compression ratio Monkey's Audio 3.80 (extra high) 21:09.65   397.89 MB 0.5097 RKAU 1.06 (normal) 54:05.71   397.96 MB 0.5098 RKAU 1.06 (high) 137:00.11   398.29 MB 0.5103 Monkey's Audio 3.80 (high) 7:59.74   404.08 MB 0.5176 LPAC 1.20 (-r, high) 91:19.47   409.72 MB 0.5249 LPAC 1.20 (-r, normal) 21:22.25   409.81 MB 0.5250 LPAC 1.20 (-r, extra high) 112:53.78   410.54 MB 0.5260 flac 0.10 (-8) 55:36.36   411.86 MB 0.5276 flac 0.10 (-5, default) 13:34.01   413.55 MB 0.5298 flac 0.10 (-3) 10:07.74   419.41 MB 0.5373 WavPack 3.6 (high) 10:21.44   420.92 MB 0.5393 Ogg Squish 0.98 ?   431.08 MB 0.5522 flac 0.10 (-1) 8:57.16   432.42 MB 0.5540 Shorten 3.2 (-p0 -b256, default) 10:05.16   433.56 MB 0.5554 Kexis 0.2.2 17:50.23   434.33 MB 0.5564 Shorten 3.2 (-p8 -b2048) 12:21.27   438.86 MB 0.5622 WaveZIP 8:41.72   452.95 MB 0.5802 RIFF WAVE     780.56 MB 1.0000

Here are the results for each individual track.

Track Codec Encode time Compressed size Compression ratio Dream Theater 6:00 58.47 MB         Monkey's Audio (extra high) 1:39.08 43.70 MB 0.7475 Monkey's Audio (high) 0:41.98 43.85 MB 0.7500 RKAU 1.06 (high) 8:12.44 43.87 MB 0.7503 RKAU 1.06 (normal) 2:59.56 43.88 MB 0.7504 flac 0.10 (-8) 4:17.32 44.33 MB 0.7581 flac 0.10 (-5, default) 1:04.43 44.40 MB 0.7594 LPAC 1.20 (-r, high) 6:51.24 44.42 MB 0.7598 LPAC 1.20 (-r, normal) 1:45.72 44.44 MB 0.7601 LPAC 1.20 (-r, extra high) 7:50.80 44.44 MB 0.7601 Shorten 3.2 (-p8 -b2048) 0:58.42 44.75 MB 0.7654 flac 0.10 (-3) 0:49.05 44.78 MB 0.7658 Ogg Squish 0.98 ? 45.17 MB 0.7725 WavPack 3.6 (high) 0:49.21 45.37 MB 0.7760 Pegasus-SPS 4:45.00 45.40 MB 0.7765 Kexis 0.2.2 1:25.04 46.52 MB 0.7956 flac 0.10 (-1) 0:44.12 46.64 MB 0.7978 Shorten 3.2 (-p0 -b256, default) 0:47.19 46.68 MB 0.7984 WaveZIP 0:38.99 47.22 MB 0.8077 Eddie Warner Titus 27.87 MB         RKAU 1.06 (high) 3:34.79 14.54 MB 0.5216 RKAU 1.06 (normal) 1:12.25 14.60 MB 0.5238 flac 0.10 (-8) 1:58.03 15.00 MB 0.5384 flac 0.10 (-5, default) 0:29.18 15.12 MB 0.5424 flac 0.10 (-3) 0:21.96 15.43 MB 0.5537 Shorten 3.2 (-p0 -b256, default) 0:20.71 15.78 MB 0.5662 Monkey's Audio (extra high) 0:45.47 16.04 MB 0.5754 Monkey's Audio (high) 0:13.99 16.11 MB 0.5779 Shorten 3.2 (-p8 -b2048) 0:26.37 16.21 MB 0.5818 flac 0.10 (-1) 0:19.24 16.38 MB 0.5879 LPAC 1.20 (-r, high) 2:59.29 16.60 MB 0.5956 LPAC 1.20 (-r, extra high) 3:24.92 16.61 MB 0.5959 LPAC 1.20 (-r, normal) 0:40.91 16.65 MB 0.5973 Ogg Squish 0.98 ? 17.03 MB 0.6112 WavPack 3.6 (high) 0:15.96 17.22 MB 0.6180 Kexis 0.2.2 0:32.81 17.40 MB 0.6242 WaveZIP 0:17.55 17.89 MB 0.6420 Tool Forty-six & 2 64.25 MB         Monkey's Audio (extra high) 1:48.94 39.30 MB 0.6116 Monkey's Audio (high) 0:33.43 39.51 MB 0.6149 RKAU 1.06 (normal) 3:34.75 39.93 MB 0.6214 RKAU 1.06 (high) 8:37.42 39.97 MB 0.6220 LPAC 1.20 (-r, normal) 1:52.22 40.57 MB 0.6314 LPAC 1.20 (-r, high) 7:36.55 40.61 MB 0.6320 LPAC 1.20 (-r, extra high) 9:49.64 40.71 MB 0.6336 flac 0.10 (-8) 4:37.56 40.88 MB 0.6363 flac 0.10 (-5, default) 1:08.85 41.04 MB 0.6387 WavPack 3.6 (high) 0:52.37 41.72 MB 0.6492 flac 0.10 (-3) 0:52.30 41.74 MB 0.6496 Ogg Squish 0.98 ? 42.27 MB 0.6578 flac 0.10 (-1) 0:46.44 42.70 MB 0.6646 Kexis 0.2.2 1:30.85 42.75 MB 0.6652 Shorten 3.2 (-p8 -b2048) 1:02.49 43.06 MB 0.6701 Shorten 3.2 (-p0 -b256, default) 0:52.06 43.18 MB 0.6721 WaveZIP 0:42.84 44.52 MB 0.6930 Cannibal Corpse Mummified In Barbed Wire 33.37 MB         Monkey's Audio (extra high) 0:49.20 23.47 MB 0.7033 Monkey's Audio (high) 0:23.25 23.66 MB 0.7087 LPAC 1.20 (-r, normal) 1:01.16 23.75 MB 0.7116 LPAC 1.20 (-r, high) 5:13.57 23.92 MB 0.7168 LPAC 1.20 (-r, extra high) 6:04.27 23.95 MB 0.7175 RKAU 1.06 (normal) 1:32.20 24.04 MB 0.7202 RKAU 1.06 (high) 3:21.70 24.04 MB 0.7202 flac 0.10 (-8) 2:26.19 24.18 MB 0.7244 flac 0.10 (-5, default) 0:36.65 24.30 MB 0.7281 Shorten 3.2 (-p8 -b2048) 0:33.98 25.12 MB 0.7526 flac 0.10 (-3) 0:27.77 25.16 MB 0.7539 Ogg Squish 0.98 ? 25.23 MB 0.7558 WavPack 3.6 (high) 0:28.07 25.44 MB 0.7621 Kexis 0.2.2 0:47.07 26.03 MB 0.7799 flac 0.10 (-1) 0:24.65 26.10 MB 0.7818 Shorten 3.2 (-p0 -b256, default) 0:27.19 26.61 MB 0.7972 WaveZIP 0:22.25 26.89 MB 0.8058 Alanis Morisette Hand In My Pocket 39.09 MB         Monkey's Audio (extra high) 1:03.98 22.85 MB 0.5845 Monkey's Audio (high) 0:25.70 23.04 MB 0.5893 RKAU 1.06 (high) 5:54.68 23.16 MB 0.5925 RKAU 1.06 (normal) 2:23.63 23.19 MB 0.5933 flac 0.10 (-8) 2:47.02 23.45 MB 0.5998 LPAC 1.20 (-r, normal) 1:07.58 23.45 MB 0.6000 LPAC 1.20 (-r, high) 4:47.03 23.49 MB 0.6008 LPAC 1.20 (-r, extra high) 5:50.53 23.52 MB 0.6016 flac 0.10 (-5, default) 0:41.39 23.56 MB 0.6026 Ogg Squish 0.98 ? 24.11 MB 0.6167 WavPack 3.6 (high) 0:31.44 24.30 MB 0.6217 flac 0.10 (-3) 0:31.19 24.32 MB 0.6220 Shorten 3.2 (-p8 -b2048) 0:37.23 24.72 MB 0.6323 Kexis 0.2.2 0:55.13 24.80 MB 0.6345 flac 0.10 (-1) 0:28.00 24.81 MB 0.6347 Shorten 3.2 (-p0 -b256, default) 0:29.82 25.34 MB 0.6481 WaveZIP 0:28.05 25.95 MB 0.6638 Gloria Estefan Conga 45.15 MB         Monkey's Audio (extra high) 1:15.79 30.12 MB 0.6670 Monkey's Audio (high) 0:29.68 30.32 MB 0.6716 flac 0.10 (-8) 3:17.05 30.75 MB 0.6811 RKAU 1.06 (high) 6:52.69 30.83 MB 0.6828 flac 0.10 (-5, default) 0:48.82 30.86 MB 0.6833 RKAU 1.06 (normal) 2:41.42 30.87 MB 0.6837 LPAC 1.20 (-r, normal) 1:20.29 31.03 MB 0.6871 WavPack 3.6 (high) 0:37.15 31.04 MB 0.6875 Ogg Squish 0.98 ? 31.06 MB 0.6879 LPAC 1.20 (-r, high) 5:33.21 31.06 MB 0.6879 LPAC 1.20 (-r, extra high) 6:39.28 31.11 MB 0.6889 flac 0.10 (-3) 0:37.11 31.63 MB 0.7006 Shorten 3.2 (-p8 -b2048) 0:44.27 31.76 MB 0.7034 Kexis 0.2.2 1:06.75 31.86 MB 0.7056 flac 0.10 (-1) 0:33.15 31.99 MB 0.7085 Shorten 3.2 (-p0 -b256, default) 0:36.39 32.47 MB 0.7191 WaveZIP 0:29.42 33.02 MB 0.7313 Cream White Room 53.01 MB         RKAU 1.06 (high) 8:15.46 34.30 MB 0.6469 RKAU 1.06 (normal) 3:12.99 34.35 MB 0.6479 Monkey's Audio (extra high) 1:28.45 34.65 MB 0.6535 Monkey's Audio (high) 0:24.17 34.91 MB 0.6586 flac 0.10 (-8) 3:50.47 35.00 MB 0.6602 LPAC 1.20 (-r, normal) 1:34.16 35.10 MB 0.6621 LPAC 1.20 (-r, high) 6:39.29 35.17 MB 0.6633 flac 0.10 (-5, default) 0:57.08 35.17 MB 0.6634 LPAC 1.20 (-r, extra high) 7:39.28 35.19 MB 0.6638 flac 0.10 (-3) 0:43.36 35.37 MB 0.6672 Shorten 3.2 (-p8 -b2048) 0:51.33 35.40 MB 0.6677 Ogg Squish 0.98 ? 35.74 MB 0.6742 WavPack 3.6 (high) 0:44.18 35.82 MB 0.6758 Shorten 3.2 (-p0 -b256, default) 0:40.76 36.42 MB 0.6870 flac 0.10 (-1) 0:37.79 36.56 MB 0.6897 Kexis 0.2.2 1:13.46 36.64 MB 0.6911 WaveZIP 0:35.77 37.13 MB 0.7004 Maurice Ravel Fanfare from "L'eventail de Jeanne" 20.82 MB         RKAU 1.06 (normal) 1:46.51 6.86 MB 0.3297 RKAU 1.06 (high) 3:53.54 6.90 MB 0.3316 Monkey's Audio (extra high) 0:30.30 7.09 MB 0.3407 LPAC 1.20 (-r, normal) 0:30.93 7.47 MB 0.3586 LPAC 1.20 (-r, extra high) 3:06.27 7.48 MB 0.3591 LPAC 1.20 (-r, high) 2:21.16 7.48 MB 0.3593 Monkey's Audio (high) 0:12.58 7.56 MB 0.3634 flac 0.10 (-8) 1:21.11 7.70 MB 0.3699 flac 0.10 (-5, default) 0:19.78 7.73 MB 0.3713 flac 0.10 (-3) 0:14.58 7.80 MB 0.3745 WavPack 3.6 (high) 0:16.11 7.99 MB 0.3838 flac 0.10 (-1) 0:12.88 8.15 MB 0.3913 Ogg Squish 0.98 ? 8.15 MB 0.3914 Shorten 3.2 (-p0 -b256, default) 0:13.68 8.19 MB 0.3932 Shorten 3.2 (-p8 -b2048) 0:17.56 8.29 MB 0.3983 Kexis 0.2.2 0:26.88 8.52 MB 0.4091 WaveZIP 0:13.11 8.72 MB 0.4193 Maurice Ravel String Quartet (4th movement) 56.18 MB         Monkey's Audio (extra high) 1:29.26 20.87 MB 0.3715 RKAU 1.06 (normal) 3:51.42 21.46 MB 0.3820 Monkey's Audio (high) 0:34.29 21.55 MB 0.3836 RKAU 1.06 (high) 10:39.05 21.56 MB 0.3838 LPAC 1.20 (-r, high) 6:28.14 22.30 MB 0.3969 LPAC 1.20 (-r, normal) 1:28.02 22.32 MB 0.3972 LPAC 1.20 (-r, extra high) 8:13.86 22.38 MB 0.3983 WavPack 3.6 (high) 0:43.84 22.53 MB 0.4010 flac 0.10 (-8) 3:57.73 22.61 MB 0.4025 flac 0.10 (-5, default) 0:56.77 22.69 MB 0.4039 flac 0.10 (-3) 0:41.85 23.22 MB 0.4133 flac 0.10 (-1) 0:36.77 23.38 MB 0.4161 Kexis 0.2.2 1:14.81 23.42 MB 0.4168 Shorten 3.2 (-p0 -b256, default) 0:40.30 23.71 MB 0.4221 Ogg Squish 0.98 ? 24.12 MB 0.4293 Shorten 3.2 (-p8 -b2048) 0:49.18 25.59 MB 0.4554 WaveZIP 0:36.60 25.84 MB 0.4600 Sergei Prokofiev Piano Concerto No.3 (3rd movement) 100.68 MB         Monkey's Audio (extra high) 2:37.54 34.55 MB 0.3431 RKAU 1.06 (normal) 6:34.97 35.31 MB 0.3507 Monkey's Audio (high) 1:00.47 35.46 MB 0.3521 LPAC 1.20 (-r, high) 10:12.47 35.74 MB 0.3549 RKAU 1.06 (high) 18:34.20 35.80 MB 0.3555 LPAC 1.20 (-r, extra high) 12:18.79 35.83 MB 0.3558 LPAC 1.20 (-r, normal) 2:33.43 36.05 MB 0.3580 WavPack 3.6 (high) 1:17.06 37.88 MB 0.3762 flac 0.10 (-8) 6:58.46 38.08 MB 0.3782 flac 0.10 (-5, default) 1:40.36 38.21 MB 0.3794 flac 0.10 (-3) 1:14.13 38.56 MB 0.3830 flac 0.10 (-1) 1:05.07 39.35 MB 0.3908 Shorten 3.2 (-p0 -b256, default) 1:12.51 39.49 MB 0.3921 Kexis 0.2.2 2:12.79 39.89 MB 0.3962 Ogg Squish 0.98 ? 41.86 MB 0.4157 WaveZIP 1:05.60 43.67 MB 0.4337 Shorten 3.2 (-p8 -b2048) 1:29.19 45.34 MB 0.4502 Frederic Chopin Prelude No.24 in d minor 27.46 MB         Monkey's Audio (extra high) 0:42.69 10.53 MB 0.3834 Monkey's Audio (high) 0:19.69 10.77 MB 0.3921 LPAC 1.20 (-r, high) 3:21.61 10.91 MB 0.3973 LPAC 1.20 (-r, normal) 0:41.79 10.92 MB 0.3976 LPAC 1.20 (-r, extra high) 3:56.36 10.93 MB 0.3979 RKAU 1.06 (normal) 1:58.42 10.97 MB 0.3994 RKAU 1.06 (high) 5:20.71 11.21 MB 0.4083 WavPack 3.6 (high) 0:22.32 11.52 MB 0.4193 flac 0.10 (-8) 1:54.37 11.69 MB 0.4255 flac 0.10 (-5, default) 0:27.77 11.72 MB 0.4266 flac 0.10 (-3) 0:20.10 11.74 MB 0.4275 flac 0.10 (-1) 0:17.50 11.86 MB 0.4320 Shorten 3.2 (-p0 -b256, default) 0:19.21 12.05 MB 0.4386 Kexis 0.2.2 0:37.61 12.14 MB 0.4419 WaveZIP 0:18.75 13.08 MB 0.4765 Ogg Squish 0.98 ? 13.31 MB 0.4845 Shorten 3.2 (-p8 -b2048) 0:24.23 14.40 MB 0.5242 Domenico Scarlatti Sonata K.42 (arr.Yepes for guitar) 16.39 MB         Monkey's Audio (extra high) 0:25.79 6.96 MB 0.4245 RKAU 1.06 (high) 3:09.40 6.96 MB 0.4246 RKAU 1.06 (normal) 1:14.43 6.97 MB 0.4252 Monkey's Audio (high) 0:10.28 7.14 MB 0.4356 LPAC 1.20 (-r, normal) 0:25.98 7.27 MB 0.4436 LPAC 1.20 (-r, high) 2:21.30 7.34 MB 0.4480 flac 0.10 (-8) 1:10.01 7.37 MB 0.4497 LPAC 1.20 (-r, extra high) 3:00.91 7.38 MB 0.4500 flac 0.10 (-5, default) 0:16.41 7.40 MB 0.4512 WavPack 3.6 (high) 0:13.17 7.41 MB 0.4520 flac 0.10 (-3) 0:12.09 7.43 MB 0.4530 Shorten 3.2 (-p0 -b256, default) 0:11.43 7.48 MB 0.4564 Kexis 0.2.2 0:21.79 7.50 MB 0.4572 flac 0.10 (-1) 0:10.48 7.53 MB 0.4590 Ogg Squish 0.98 ? 7.74 MB 0.4723 WaveZIP 0:10.56 7.83 MB 0.4781 Shorten 3.2 (-p8 -b2048) 0:14.59 8.20 MB 0.5004 The Benedictine Monks of Santo Domingo de Silos Laetatus sum 24.26 MB         RKAU 1.06 (high) 3:15.29 12.21 MB 0.5031 RKAU 1.06 (normal) 1:25.48 12.21 MB 0.5034 Monkey's Audio (extra high) 0:41.19 12.47 MB 0.5138 Monkey's Audio (high) 0:15.69 12.68 MB 0.5228 LPAC 1.20 (-r, normal) 0:41.22 12.75 MB 0.5253 flac 0.10 (-8) 1:44.85 12.82 MB 0.5285 LPAC 1.20 (-r, high) 3:40.65 12.88 MB 0.5309 LPAC 1.20 (-r, extra high) 4:53.81 12.92 MB 0.5323 flac 0.10 (-5, default) 0:25.63 12.92 MB 0.5324 flac 0.10 (-3) 0:18.56 12.98 MB 0.5349 WavPack 3.6 (high) 0:20.21 13.15 MB 0.5420 Kexis 0.2.2 0:34.04 13.30 MB 0.5481 Shorten 3.2 (-p0 -b256, default) 0:17.87 13.32 MB 0.5489 flac 0.10 (-1) 0:16.33 13.34 MB 0.5499 Shorten 3.2 (-p8 -b2048) 0:22.18 13.42 MB 0.5531 Ogg Squish 0.98 ? 13.41 MB 0.5528 WaveZIP 0:16.37 13.72 MB 0.5655 L. Subramaniam Raga Sivapriya 213.56 MB         RKAU 1.06 (high) 47:18.78 92.94 MB 0.4351 RKAU 1.06 (normal) 19:37.68 93.31 MB 0.4369 Monkey's Audio (extra high) 5:51.97 95.30 MB 0.4462 Monkey's Audio (high) 2:14.54 97.52 MB 0.4566 LPAC 1.20 (-r, high) 23:13.96 97.80 MB 0.4579 flac 0.10 (-8) 15:16.19 97.99 MB 0.4588 LPAC 1.20 (-r, normal) 5:46.84 98.04 MB 0.4590 LPAC 1.20 (-r, extra high) 30:04.06 98.10 MB 0.4593 flac 0.10 (-5, default) 3:40.89 98.44 MB 0.4609 flac 0.10 (-3) 2:43.69 99.25 MB 0.4647 WavPack 3.6 (high) 2:50.35 99.53 MB 0.4660 Ogg Squish 0.98 ? 101.88 MB 0.4770 Shorten 3.2 (-p8 -b2048) 3:30.25 102.60 MB 0.4804 Shorten 3.2 (-p0 -b256, default) 2:56.04 102.84 MB 0.4815 Kexis 0.2.2 4:51.20 103.57 MB 0.4849 flac 0.10 (-1) 2:24.74 103.63 MB 0.4852 WaveZIP 2:25.86 107.47 MB 0.5032