CompuServe Messages

Jeff, Sorry for replying you late, I was so busy. Put it into the simplest way of speaking: M-JPEG is just a sequence of JPEG compressed frames. JPEG compression is also balance, that means its compression and decompression take equal time. You can extract and locate each frame percisely, therefore, you can use this format (among other formats) to do video frame editing. MPEG and other compression scheme (for example, CinaPak and Indeo) use key frames concept and do further compression by only recording the delta to the key frame. MPEG go even further by recording the delta to the delta and/or also considering all the frames/deltas. Its speed is also not balance, normally its compression will take around 100 times more than the decompression. And, its decompression is time and data dependent. If you move a frame forward or remove/loss a frame, all will be affected/distorted. Therefore, to locate a precise frame to do editing or move a frame will become not practical/possible without hardware assistance. However, as you said, if each frame of MPEG is set to be a key frame (I-Frame), MPEG/M-JPEG will be the same. But, you loss the extra compression gain in MPEG. Therefore, it is possible to do I-Frame only MPEG clip editing but we need to do/define the rule to do interpolation of those delta frames without much performance penalty for practical usage. This kind of editable MPEG format is only in a early draft poposal stage. Right now, you should treat MPEG as an delivery format for your final result. And treat M-JPEG as the editable format for your source clips. Hope this will help. And, thanks for the testing you did in the New Media article. It's a very good review and reference of the exiting boards. –Vince Ulead Systems, Inc.