Hi. I'm new to digital video. Recently I bought a camcorder and shot about 10 hours of stuff while travelling. I fed the footage via a firewire link to my computer using Ulead Video Studio 7. (I know there are more sophisticated programs out there, but for my first stages this is just fine). I noticed that the resultant AVI files were mammoth -- about 1 gigabyte per 10 minutes of footage. So after transfering I converted the file to MPEG2. I did this with all 10 hours of footage. As I was preparing to get down to editing, I came across this comment from forum member vurbal: "Encoding to MPEG should always be the last step." Why is this? What advantages are there to keeping it in such an unwieldy format as AVI? Does mpeg conversion degrade quality? If so, I'll re-transfer my video and save it as AVI, but only if I have to . Could someone please advise?
Well since I was the one who made the comment, I should explain what I meant. There are 2 types of (lossy) compression that can be applied to video - Intraframe and Interframe. With intraframe compression, each frame contains all the information needed to display it, but the chroma (color) information isn't contained in every pixel so it's still smaller than the original. Both DV and MPEG use this type of compression. MPEG also uses interframe compression, meaning that only some of the frames contain all the information required for display. These are called keyframes, or in the case of MPEG, I frames. They're grouped together with several subsequent frames (B and P frames) in what's called a GOP (Group Of Pictures). To display a frame in the middle of a GOP, you need to have at least all the previous frames in that GOP, and sometimes some from the next GOP. If you edit a file with only intraframe compression applied, you can cut it at any spot without worrying about other frames, but if you cut an MPEG you have to either make sure it's on a keyframe. On a DVD, for example, there are at least 12 frames in each GOP, so if you want frame 5 out of the GOP you either need to cut at the previous or following I frame or else you'll have to re-encode because there will be B frames that require future (that's right - future) frames to be decoded first and if you remove the future frames, the MPEG decoder doesn't have all the information needed to decode B frames that depend on them. The one exception to this (that I know of) is a program called Womble MPEG VCR. There's another Womble program that I can't remember the name of right now, and I believe it can also cut on any frame. Part of the "magic" Womble uses is to change open GOPs to closed GOPs. That means that no frame in the GOP requires any frame outside the GOP to be decoded. It's a somewhat confusing concept (I got a little confused typing this), but in general, the key is that you can edit MPEGs accurately with a frame accurate editor (Womble), but not with a GOP accurate editor (every other consumer editor as far as I know). _X_X_X_X_X_[small]Build a man a fire and he'll be warm for a night. Set him on fire and he'll be warm for the rest of his life Backup A DVD With DVD Rebuilder & CCE Basic: http://www.afterdawn.com/guides/archive/dvd_rebuilder_tutorial.cfm[/small]
Hi guys, Yep, those .avis are really big so I don't try and download the entire thing. Being a relative newbie to camcorders, I have a lot of footage that I really don't want on my finished product. I do most of my editing while capturing. You spend a lot of time watching and taking notes but it sure saves encoding time later. I try and save about 25-30% of my footage. But like I said my camera work is not that great. It looks a lot better though, after some serious editing. vurbal, You are the man when it comes to this sort of thing, I did want to say how amazing the GOP function is. By understanding this process a person can see why encoding is such a resource intensive and time consuming operation. A good way to see "I-frame" editing is by using the start/end feature in Shrink. it has a 14 frame resolution in most cases, which corresponds to the allowed I-frame cut points. This is even clearer in TMPGEnc DVD author, just notice where you are allowed to make your cuts. Just my $00.02 worth...
The best application I've found to look at how MPEGs (and especially B frames) work is an Elecard program called MPEG Stream Eye. It's kind of like Bitrate viewer, which is why I got it to begin with, but my favorite feature is the ability to set it to step through frames in decoder order. You can see as it skips ahead to decode the frames that B frames need to be decoded. Unfortunately I can't find any mention of it on their site now. It's a lot easier to understand if you can see it. It's hard to explain without pictures. Maybe I'll post a screen shot to make it a little clearer for anyone who reads this.
Vurbal...I'm also new to DV...and had questions along the same line. Your explanantion on inter and intraframe was very informative...and I've saved it. I think that I am so new to DV though, that I don't quite understand what your answer is to the question about the "best dv format" to use for editing? Could you recommend the process along with the S/W to use? I'm willing to spend the money on anything that works. I've read through so many posts I'm suffering from overload. It reminds me of the DVD backup days before DVDXCopy and DVD2One came along!!!
Actually I'm pretty new to DV as well, but I've been playing with Vegas Video at a friend's house, and if you have the money to spend on it I highly recommend it. My friend and I both found the interface very intuitive and easy to use, although he's used it a lot more than me since I don't have my own copy yet. One of the features I really like is the abililty to automatically create separate video files for each time you started and stopped recording. I think it sells for around $500-$600, and if you can spend a couple hundred more you can also get DVD Architect with it. DVD Architect uses the MainConcept MPEG encoder, which I'd say is the second best one there is (after CCE). I have to get going, so I'll finish this later, but like I said, if you can spend the money you should give Vegas a try. I think you'll be very happy with it.
vurbal...thanks for the reply. I have a friend who gave up on video willing to sell me his Vegas Video 4 + DVD for a reasonable price (also available on ebay for $200-300). He tells me, though, that he doesn't think it is supported any longer...that it originated with Sonic Foundry, was bought by Sony, and then dropped??? I also gave up about a year ago after buying some Pinnacle products that I couldn't get to work (synch mainly), and couldn't get support for from Pinnacle. I was using analog video as the source then, but have now changed to DV. So, with regard to Vegas, is the process here to d/l the video stream via the 1394 directly into Vegas for editing? And then I will be editing an .avi file that, when finished, will be synch'd, and Vegas will then convert to MPEG 1 or 2? Or, have I over-simplified things?
Well, the way my friend does it is to transfer from the camcorder and do his editing in Vegas and then save it, and then he opens DVD Architect and authors the DVD from the edited video. I haven't really looked at DVD Architect too closely since I do my encoding with CCE and then author with DVD-Lab, but from what he says it's pretty easy. And he knows a lot less about digital video than I do. _X_X_X_X_X_[small]In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move. Backup A DVD With DVD Rebuilder & CCE Basic: http://www.afterdawn.com/guides/archive/dvd_rebuilder_tutorial.cfm[/small]
Thanks. Now that I have some direction, I'm going to get some softwares ready over the next couple of weeks, and I will let you know how it went.
