> > IMHO, plus points for the Sony include no-light nightshot for your Blair > Witch-style fun, and a (albeit low-rent) Carl Zeiss lens. The audio jack is > the main selling point for me though. > > "...the GOP length will affect the ability to edit the output." > > I've never really understood GOP (I know it's to do with interlacing, > right?) - could you point me in the direction of a clear explanation please? > > > > No, nothing to do with interlacing (i.e. you have a GOP with any MPEG > interlaced or progressive video) > > It is the Group of Pictures. In MPEG you can encode each frame as > I-Frames, P-Frames or B-Frames. I-Frames have the complete image, P-Frames > are predicted based upon changes from an I-Frame or previous P-Frame. > B-Frames are similar to P-Frames, but bi-directionally predicted (n.b. this > implies out of order frame encoding in the encoder) from I, P and B-Frames. > A GOP is a sequence of I, P and B-Frames e.g. IBBPBBPBBPBB > > The GOP length is the number of frames between successive I-Frames. A long > GOP length will, for example, cause a delay on video appearing on changing > channels on a STB or, as editing cuts can only start from an I-Frame will > mean you can't do frame accurate editing. > > Broadcast contributions e.g. DV, use I-Frame only codecs to allow frame > accurate editing. >
Usually when taped MPEG is transferred to an online medium, the frame headers have "trick mode" data added to them to allow the frames to be found quickly for faster reconstruction. > > > > > -- > ------------------------------ > *Simon Thompson MEng MIET * > Research Engineer (Electronics) > PRINCE2TM Registered Practitioner > > *BBC Future Media and Technology* > > -- Brian Butterworth http://www.ukfree.tv - independent digital television and switchover advice, since 2002
