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 Shorten) are truly free. 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.
• 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, etc). There are 13 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 and transmitting the LPC coefficients is not very good which is the main reason why the fixed predictors 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.

Encoder Encode time Compressed size Compression ratio Monkey's Audio 3.80 (extra high) 20:24.18 381.85 MB 0.5073 RKAU 1.06 (normal) 52:53.46 383.36 MB 0.5093 RKAU 1.06 (high) 133:25.36 383.75 MB 0.5098 Monkey's Audio 3.80 (high) 7:45.75 387.97 MB 0.5154 LPAC 1.20 (-r, normal) 20:49.34 393.16 MB 0.5223 LPAC 1.20 (-r, high) 88:20.18 393.12 MB 0.5223 LPAC 1.20 (-r, extra high) 109:27.86 393.93 MB 0.5234 flac 0.6 (-6) 17:40.93 397.99 MB 0.5287 WavPack 3.6 (high) 10:05.48 403.70 MB 0.5363 Kexis 0.2.2 17:17.42 416.93 MB 0.5539 Shorten 2.3a (-p0 -b1024) 6:41.17 417.24 MB 0.5543 Shorten 2.3a (-p8 -b2048) 9:16.47 422.59 MB 0.5614 WaveZIP 8:24.17 435.06 MB 0.5780

Here are the results for each individual track.

Track Encoder 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 0.6 (-6) 1:23.89 44.38 MB 0.7590 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 2.3a (-p8 -b2048) 0:47.79 44.74 MB 0.7653 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 Shorten 2.3a (-p0 -b1024) 0:34.50 46.68 MB 0.7984 WaveZIP 0:38.99 47.22 MB 0.8077 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 0.6 (-6) 1:35.05 40.99 MB 0.6380 WavPack 3.6 (high) 0:52.37 41.72 MB 0.6492 Kexis 0.2.2 1:30.85 42.75 MB 0.6652 Shorten 2.3a (-p8 -b2048) 0:50.22 43.05 MB 0.6701 Shorten 2.3a (-p0 -b1024) 0:35.93 43.19 MB 0.6722 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 0.6 (-6) 0:48.58 24.31 MB 0.7284 Shorten 2.3a (-p8 -b2048) 0:27.03 25.12 MB 0.7525 WavPack 3.6 (high) 0:28.07 25.44 MB 0.7621 Kexis 0.2.2 0:47.07 26.03 MB 0.7799 Shorten 2.3a (-p0 -b1024) 0:19.85 26.59 MB 0.7966 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 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 0.6 (-6) 0:56.04 23.53 MB 0.6019 WavPack 3.6 (high) 0:31.44 24.30 MB 0.6217 Shorten 2.3a (-p8 -b2048) 0:30.45 24.72 MB 0.6324 Kexis 0.2.2 0:55.13 24.80 MB 0.6345 Shorten 2.3a (-p0 -b1024) 0:21.93 25.33 MB 0.6478 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 0.6 (-6) 1:06.63 30.80 MB 0.6822 RKAU 1.06 (high) 6:52.69 30.83 MB 0.6828 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 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 Shorten 2.3a (-p8 -b2048) 0:35.51 31.76 MB 0.7033 Kexis 0.2.2 1:06.75 31.86 MB 0.7056 Shorten 2.3a (-p0 -b1024) 0:24.65 32.62 MB 0.7223 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 LPAC 1.20 (-r, normal) 1:34.16 35.10 MB 0.6621 flac 0.6 (-6) 1:17.14 35.15 MB 0.6630 LPAC 1.20 (-r, high) 6:39.29 35.17 MB 0.6633 LPAC 1.20 (-r, extra high) 7:39.28 35.19 MB 0.6638 Shorten 2.3a (-p8 -b2048) 0:40.44 35.39 MB 0.6676 WavPack 3.6 (high) 0:44.18 35.82 MB 0.6758 Shorten 2.3a (-p0 -b1024) 0:29.49 36.39 MB 0.6864 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 0.6 (-6) 0:27.39 7.71 MB 0.3703 WavPack 3.6 (high) 0:16.11 7.99 MB 0.3838 Shorten 2.3a (-p0 -b1024) 0:07.92 8.16 MB 0.3921 Shorten 2.3a (-p8 -b2048) 0:13.88 8.28 MB 0.3977 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 0.6 (-6) 1:17.20 22.69 MB 0.4038 Kexis 0.2.2 1:14.81 23.42 MB 0.4168 Shorten 2.3a (-p0 -b1024) 0:29.33 23.63 MB 0.4205 Shorten 2.3a (-p8 -b2048) 0:38.05 25.58 MB 0.4552 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 0.6 (-6) 2:16.02 38.15 MB 0.3788 Shorten 2.3a (-p0 -b1024) 0:50.03 39.34 MB 0.3907 Kexis 0.2.2 2:12.79 39.89 MB 0.3962 WaveZIP 1:05.60 43.67 MB 0.4337 Shorten 2.3a (-p8 -b2048) 1:09.86 45.36 MB 0.4505 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 0.6 (-6) 0:35.24 11.70 MB 0.4261 Shorten 2.3a (-p0 -b1024) 0:13.56 12.01 MB 0.4374 Kexis 0.2.2 0:37.61 12.14 MB 0.4419 WaveZIP 0:18.75 13.08 MB 0.4765 Shorten 2.3a (-p8 -b2048) 0:20.61 14.39 MB 0.5239 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 LPAC 1.20 (-r, extra high) 3:00.91 7.38 MB 0.4500 flac 0.6 (-6) 0:22.56 7.38 MB 0.4504 WavPack 3.6 (high) 0:13.17 7.41 MB 0.4520 Shorten 2.3a (-p0 -b1024) 0:07.99 7.47 MB 0.4558 Kexis 0.2.2 0:21.79 7.50 MB 0.4572 WaveZIP 0:10.56 7.83 MB 0.4781 Shorten 2.3a (-p8 -b2048) 0:10.91 8.20 MB 0.5001 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 LPAC 1.20 (-r, high) 3:40.65 12.88 MB 0.5309 flac 0.6 (-6) 0:34.24 12.90 MB 0.5318 LPAC 1.20 (-r, extra high) 4:53.81 12.92 MB 0.5323 WavPack 3.6 (high) 0:20.21 13.15 MB 0.5420 Shorten 2.3a (-p0 -b1024) 0:12.71 13.28 MB 0.5475 Kexis 0.2.2 0:34.04 13.30 MB 0.5481 Shorten 2.3a (-p8 -b2048) 0:17.35 13.41 MB 0.5527 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 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 0.6 (-6) 5:00.95 98.29 MB 0.4602 WavPack 3.6 (high) 2:50.35 99.53 MB 0.4660 Shorten 2.3a (-p0 -b1024) 1:53.28 102.54 MB 0.4801 Shorten 2.3a (-p8 -b2048) 2:34.37 102.59 MB 0.4803 Kexis 0.2.2 4:51.20 103.57 MB 0.4849 WaveZIP 2:25.86 107.47 MB 0.5032