Article: 695 of alt.fan.mike-jittlov From: Rombaldi Newsgroups: alt.fan.mike-jittlov Subject: Re: Argh! Who telecined this darned movie?! Message-ID: References: <4leeav8b4sjrnc2ssufij4s3vo8g9g96hg@4ax.com> <63vfav85krm7hd60scdsdgbobkhhd9sigj@4ax.com> X-Newsreader: Forte Agent 1.92/32.572 X-No-Archive: yes MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 143 X-Complaints-To: abuse@easynews.com Organization: EasyNews, UseNet made Easy! - Test our service with our FREE trial at https://www.easynews.com/trial/trial.phtml X-Complaints-Info: Please be sure to forward a copy of ALL headers otherwise we will be unable to process your complaint properly. Date: Thu, 24 Apr 2003 16:19:24 GMT Path: news.meer.net!sea-read.news.verio.net!dfw-artgen!iad-peer.news.verio.net!news.verio.net!skynet.be!skynet.be!newsfeed.news2me.com!newsfeed2.easynews.com!easynews.com!easynews!easynews-local!post-03.news.easynews.com.POSTED!not-for-mail Xref: archive.mv.meer.net alt.fan.mike-jittlov:695 On Thu, 24 Apr 2003 11:04:39 -0400, Neil Nadelman wrote: > Well, the problem with that theory is that I remember when >Rombaldi laid out what equipment he bought months ago to make these >DVDs, and it included a Panasonic set top DVD recorder, along with a >DVD-RAM/DVD-R drive for his computer to take in the captured video for >authoring. THis would mean that he captured it as MPEG-2 first and >then used the files in Ulead DVD Workshop to make the menus and render >the final DVD image. In that case, I wonder how good the side flip >edit is. > > Rombaldi? Could you illuminute this question, please? > (takes out the Flashlight of Truth and Wisdom).. Well.. yes, it's using the Panasonic DMR-E20 recorder sourced form the Laserdisc.. and I don't know WHY people keep perpuating they myth that "MPEG2 can not be edited"... To mangle Klatuu.. "I find it works well enough to splice two halfs of a disc together" Now, if you plan on doing MASSIVE editing (fades, transitions, title overlays, key inserts and the like).. then yes you should be capturing to an (relatively less) compressed format (ie. DV) and then use a software and/or hardware encoder to get it down to DVD Compliant MPEG2 . But you CAN do relatively low level editing on MPEG2 files (trims, joins and re-arrangement of scenes) ie. commercial editing and 'disc flips'. The trick is to find an editor that (a) will 'smart-render' and (b) not muck up the audio... defining 'smart render' (warning, engaging techie mode).. an MPEG2 stream consists of FRAMES of picture information... I-Frames are the full, unmolested picture with no information lost. Call it a 35mm slide. P-Frame is a 'PREDICTED' frame, it is generated from the estimation of the motion vectors in the picture behind it. B-Frames are BI-DIRECTIONAL PREDICTED frames or BETWEEN frames.. they are generated from information both AHEAD and BEHIND of the current frames. These frames are put together in GROUPS OF PICTURES or GOPs. For DVD and editing work, they should be CLOSED GOPS that end with the final frame being a B-Frame that uses ONLY the previous frames as reference... A sequence looks like this.... I B B B B P B B B P B B B P and the complete stream looks like this... IBBPBBPBBPBB IBBPBBPBB IBBPBBPBB IBBPBB A GOP can be a variable number of frames, up to a max of 18 frames (or is it 15? One is NTSC the other is PAL.. anyway..) There are several ways of editing an MPEG2 file. One is GOP accurate.... let's say we have this... I B B P B B P B B P I B* B* P* B* B P B B P I B B P B B P we want to remove the frames marked with a * in a GOP accurate editor we would lose the entire middle GOP I B B P B B P B B P I B B P B B P which in this case, we only wanted to remove 4 frames, but lost 10. Perhaps ok for clippiing commercials, but you could end up with either having a few frames missing from the program or a few frames of unwanted material left in... method is the brute force or hard join 'frame accurate' edit I B B P B B P B B P I B B P B B P B B* P* I* B* B* P B B P again, we'll remove the frames marked with an * to get this... I B B P B B P B B P I B B P B B P b p B B P (the lowercase b and p showing where the join is) TWO problem here... one is the 'b' where the join is. since it's a BI-DIRECTIONAL predictive frame... where's the 'right' side of the predicted frame? It's gone.. so you may end up with a distortion, jump, jiggle or just plain 'it aint' right' spot on th edit... now, if you are clipping commercials and it's mostly black on both sides.. you may get away with it.. HOWEVER.. there is the chance that you could end up with a GOP that is TOO LONG. Let's say you have two GOPs, one is 15 frames long and the next is 13 frames. We shall remove 2 frames from the end of the first and 3 from then beginning of the second... leaving us with a GOP that is 23 frames long. Outside of spec and (depending on the implementation of the codec in the playback device) could stutter, skip or just plain fall down go boom. THE PROPER WAY to do it is a 'smart-rendering/re-encode' frame accurate edit... let's take the above again.... I B B P B B P B B P I B B P B B P B B* P* I* B* B* P B B P when outputing the edited file, the editor first RE-CONSTRUCT the frames BEFORE removing them... I B B P B B P B B P I B B P B B P R R* R* R* R* R* R R R R the R's are the FULL UNCOMPRESSED FRAMES, note that it reconstructs to the END of the last GOP and slightly BEFORE the edit. We now REMOVE the frames we want rid of I B B P B B P B B P I B B P B B P R R R R R and RE-ENCODE the GOP sequence PROPERLY I B B P B B P B B P I B B P B B P B B P B B the GOP structure integrity is maintained, we don't have any distortions or jitters in the picture, it dosen't matter what the context is on either side of the clip and the GOP length stays within specs, We don't disturb anything outside the edit point. And the flipping of the disc disappears.... To My Knowledge, the only editing program that does this right (at anything resembling a reasonable cost) is Womble MPEG2VCR. I shall leave the concepts of keeping audio in sync during all the above as an exercise to the reader that has a good supply of Excedrine.