Windows Media Centre (Windows 7 version) records TV shows as WTV files. This is a Microsoft format and contains audio, video and metadata.
Unfortunately Microsoft don't appear to have provided any easy way of editing, trimming, cutting or converting these files. If you record a TV programme and want to remove the junk at the start and end or want to remove commercial breaks you are stuffed.
So can it be done?
I spent ages trying to answer this question. There are a number of solutions out there but here is the one I would recommend.
Stage 1 - Convert WTV file to DVR-MS
In Windows file explorer right click on the WTV file and select "Convert to .dvr-ms Format". This is will convert the WTV format to the slightly older DVR-MS format as used in previous versions of Windows Media Center.
Stage 2 - Convert to MPEG2
To convert to a standard MPEG2 file you can use DVRMSToolbox available from andy vt's tools & blog. Use the DVRMStoMPEGGUI utility. Set the profile to "Convert DVR-MS file to MPEG".
Stage 3 - Edit/Trim & Export
Now you've got an MPEG2 file you can use any MPEG2 compliant tool to edit or trim out sections you don't want.
I use Womble MPEG Video Wizard because it allows frame accurate editing of MPEG video. Once you have made the changes you can export a fresh MPEG2 file without re-encoding. This means there is no loss of quality.