What can be done with .CPI or .clpi files?
As Professor Sparkles has correctly pointed out (I've just checked and confirm) — the MediaInfo tool can extract some metadata from these files. Here is a sample output from one of mine:

General
Complete name                            : /Volumes/CAM_SD/PRIVATE/AVCHD/BDMV/CLIPINF/00119.CPI
Format                                   : Blu-ray Clip info
File size                                : 502 Bytes

Video
ID                                       : 4113 (0x1011)
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 50.000 fps

Audio
ID                                       : 4352 (0x1100)
Format                                   : AC-3
Format/Info                              : Audio Coding 3
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Language                                 : English

Text
ID                                       : 4608 (0x1200)
Format                                   : PGS
Language                                 : English


(But note that it can output more details in the --full mode.)

Also, it may be helpful to note that the AVCHD standard is proprietary and its spec is not publicly available. Attempts to reverse-engineer its components exist, and one of them is in this forum thread (from 2008): http://forum.doom9.org/showthread.php?t=141361