Bad news. I've now discovered that depending on the channel recorded, there can be different and significant "drift" and/or "offsets".

I'll examing this file a little more and post back, but I've just tried to watch Monster Garage, recorded from Discovery HD. Even the very first commercial is way off and by the end of the show the error is huge.

If I look at the file properties in Microsoft's Explorer, it says the recording has a length of 1:04:54. Also when I play the show in Media Center it does end at 1 hour, 4 minutes and 54 seconds (at least according to the progress bar in Media Center).

Looking at the log file from Show Analyzer, the last segment of the show is supposed to end at 1:05:24.236. This is a full 30 seconds past the end of the show. As you can probably guess, the commercial skipping doesn't exactly work very well...

One thing I do want to do is examine the recording a little and make sure that there isn't some sort of glitch in the recording itself. I'll post back with information on that, but for now, here is a portion of the recording log:

This log created by ShowAnalyzer v0.9.7
01:48:50(0) Setting path to: "e:\recorded tv\Fire Monster Garage_TDCHD_14_04_2008_21_58_01.dvr-ms"
01:48:51(0) The Automatic Profile Selection indicated that the "HD Channels" profile should be used.
Start Time End Time Length Divider AR EP Captions Score Verdict Debug Bits
-----------------------------------------------------------------------------------------------------------------------
0:00:00.000 0:01:49.876 0:01:49.893 START OF VIDEO 1.79772 0 UNKNOWN 20 Show 000100000000 000001
0:01:49.893 0:01:52.378 0:00:02.502 BLANK FRAME -1.#IND 0 UNKNOWN 40 Comm 010100000100 100000
0:01:52.395 0:02:02.405 0:00:10.026 BLANK FRAME 1.79772 0 UNKNOWN 30 Comm 000100010000 010000
0:02:02.422 0:02:12.599 0:00:10.193 BLANK FRAME 1.79772 0 UNKNOWN 30 Comm 000100010000 010000
0:02:12.615 0:04:14.837 0:02:02.238 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:04:14.854 0:14:27.866 0:10:13.029 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:14:27.883 0:14:33.022 0:00:05.155 BLANK FRAME 1.50078 0 UNKNOWN 60 Comm 010100010000 100000
0:14:33.038 0:15:03.152 0:00:30.130 BLANK FRAME 1.35135 0 UNKNOWN 80 Comm 010101000000 010000
0:15:03.168 0:15:33.666 0:00:30.513 BLANK FRAME 1.79772 0 UNKNOWN 40 Comm 000101000000 010000
0:15:33.682 0:16:04.179 0:00:30.513 BLANK FRAME 1.35755 0 UNKNOWN 80 Comm 010101000000 010000
0:16:04.196 0:23:28.640 0:07:24.460 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:23:28.657 0:23:58.970 0:00:30.330 BLANK FRAME 1.72172 0 UNKNOWN 80 Comm 010101000000 100000
0:23:58.987 0:24:31.369 0:00:32.399 BLANK FRAME 1.68421 0 UNKNOWN 40 Comm 010100000010 010000
0:24:31.386 0:25:01.900 0:00:30.530 BLANK FRAME 1.79516 0 UNKNOWN 40 Comm 000101000000 010000
0:25:01.917 0:28:13.058 0:03:11.157 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:28:13.074 0:30:05.553 0:01:52.495 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:30:05.570 0:30:20.718 0:00:15.165 BLANK FRAME 1.35989 0 UNKNOWN 80 Comm 010101000000 100000
0:30:20.735 0:30:52.033 0:00:31.314 BLANK FRAME 1.37037 0 UNKNOWN 40 Comm 010100000010 010000
0:30:52.050 0:31:22.397 0:00:30.363 BLANK FRAME 1.36273 0 UNKNOWN 80 Comm 010101000000 010000
0:31:22.413 0:31:52.860 0:00:30.463 BLANK FRAME 1.69258 0 UNKNOWN 80 Comm 010101000000 010000
0:31:52.877 0:37:29.814 0:05:36.953 BLANK FRAME 1.79516 1 UNKNOWN 0.1 Show 000010000001 000001
0:37:29.830 0:37:34.952 0:00:05.138 BLANK FRAME 1.74317 0 UNKNOWN 60 Comm 010100010000 100000
0:37:34.969 0:38:06.067 0:00:31.114 BLANK FRAME 1.80603 0 UNKNOWN 40 Comm 010100000010 010000
0:38:06.083 0:38:36.530 0:00:30.463 BLANK FRAME 1.79772 0 UNKNOWN 40 Comm 000101000000 010000
0:38:36.547 0:39:06.894 0:00:30.363 BLANK FRAME 1.35562 0 UNKNOWN 80 Comm 010101000000 010000
0:39:06.911 0:49:54.975 0:10:48.080 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:49:54.992 0:50:00.113 0:00:05.138 BLANK FRAME 1.47312 0 UNKNOWN 60 Comm 010100010000 100000
0:50:00.130 0:50:31.862 0:00:31.748 BLANK FRAME 1.34758 0 UNKNOWN 40 Comm 010100000010 010000
0:50:31.878 0:51:02.192 0:00:30.330 BLANK FRAME 1.36752 0 UNKNOWN 80 Comm 010101000000 010000
0:51:02.209 0:52:02.619 0:01:00.427 BLANK FRAME 1.79772 0 UNKNOWN 40 Comm 000101000000 010000
0:52:02.636 0:52:13.413 0:00:10.794 BLANK FRAME 1.79772 0 UNKNOWN 30 Comm 000100010000 010000
0:52:13.430 0:57:32.715 0:05:19.302 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
0:57:32.732 1:02:13.513 0:04:40.797 BLANK FRAME 1.79772 0 UNKNOWN 2 Show 000100000001 000001
1:02:13.529 1:02:24.407 0:00:10.894 BLANK FRAME 1.79915 0 UNKNOWN 30 Comm 000100010000 100000
1:02:24.424 1:02:34.667 0:00:10.260 BLANK FRAME 1.79772 0 UNKNOWN 30 Comm 000100010000 010000
1:02:34.684 1:05:24.236 0:02:49.569 BLANK FRAME 1.79772 1 UNKNOWN 0.1 Show 000010000001 000001
1:05:24.253 1:05:24.253 0:00:00.000 -1.#IND -1 UNKNOWN 10 Show 000000000000 000000
02:13:53(0) Final results:
Commercial? Start End Length
-------------------------------------------------------------------
Show 0:00:00.000 0:14:27.933 0:14:27.933
Commercial 0:14:27.950 0:16:04.513 0:01:36.563
Show 0:16:04.530 0:23:28.790 0:07:24.260
Commercial 0:23:28.807 0:25:02.284 0:01:33.476
Show 0:25:02.300 0:30:05.637 0:05:03.336
Commercial 0:30:05.653 0:31:53.227 0:01:47.574
Show 0:31:53.244 0:37:29.897 0:05:36.652
Commercial 0:37:29.914 0:39:07.261 0:01:37.347
Show 0:39:07.278 0:49:55.042 0:10:47.763
Commercial 0:49:55.058 0:52:13.663 0:02:18.605
Show 0:52:13.680 1:05:24.253 0:13:10.573