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| cosmic |
| Posted: Feb 10 2003, 10:57 AM |
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Unregistered
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Hi, I am new to video, but I tried essentially postprocessing DivX or MPEG and now am able to do some capture.
I create my own SVCDs with what I have reprocessing DivX or mastering my own captures.
Every time I open the video compression dialog I wonder what should I choose.
I am sticking with DivX 5.0.3 pro that does a good job for keeping movies on the hard disk, but I guess it is not the best I should choose for cutting and pasting (I use MS Movie Maker because it looks simple enough). Huffyuv sounds interesting for the purpose of editing.
I would like to learn more on the architecture of video, how the codecs fit in, what do the standard codec do. For Example, Indeo doed MPEG?
All in all I would like to see a starting point for exploration and collection of knowledge on codecs and why we should care. |
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| Steve1138 |
| Posted: Mar 7 2003, 07:21 AM |
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from what I've read, the general opinion is to use PIC video (Pegasus imaging) codec and YUY2 format. (I use it at quality = 19, as qlty 20 is a bit better but files are almost twice the size.
RGB24 is apparently calculated FROM the YUY2 values so it doesn't make sense.
HuffYUV files are bigger than those from PICvideo. You have to register PIC for 18 USD to eliminate the overlay logo... but so what ?
Capture to AVI with the PIC first and then post convert to DivX with VD.
If you capture direct to DivX it requires more CPU% and depending on yr machine you may have higher risk of dropped frames.
(in my limited experience)
Steve
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| David.Bucci |
| Posted: Mar 9 2003, 06:05 AM |
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Lemme take a crack at it, others can pile on to fill out where i don't know things.
First, there are two categories of compression, lossless and lossy. The lossless kind shrink the # of bytes needed to store the video without losing any of the information. The main entrants in this category are:
- MJPEG type codecs, that basically do a lossless JPEG compress on each frame of video -- PicVideo, MJPEG, etc.
- HuffyUV - unsure of how it compresses
These give some compression, but not as much as the next family. That's the lossy codecs ... they compress by using various techniquest that reduce file size, but as a result some information is lost from the video. The quality of the compression scheme, in general, is determined by how well it throws away info without affecting the visual experience of the user. This all has to do with signal processing techniques, etc., that only heroes like phaeron fully understand 
Among these codecs are the MPEG4 variants (MPEG = Motion Picture Experts Group, bunch of people who make smart technical decisions and questionable business decisions ) -- these are fairly new, and include:
- DivX5
- Xvid (research project, not meant for production use)
- QuickTime 6
Before that there were MPEG2 and 1 --- these were developed in part as enabling standards for digital transmission (early satellite tv was transmitted as MPEG1 [i think] then MPEG2), and was also adopted for other purposes, e.g., all DVDs use MPEG2, Video CDs use MPEG1.
There there are all the proprietary codecs, that use company-owned algorithms. Roughly speaking:
- Microsoft's Windows Media (WMV), and before that ASF ... unsure of compression technique
- MPEG4 v3, 2, 1 ... earlier Microsfot attempts
- Real's Realvideo 9, 8, etc. standards ... again, unsure of techniques involved
- Indeo -- older standard, wavelet based, iirc (wavelets are a different signal analysis tool, that have tradeoffs with the techniques used in other codecs)
There are others, but that gives you an idea. Btw, things like "AVI" and "MOV" are technically container standards, i.e., they give you a format for holding together video and audio, each compressed using whatever technique ... so an AVI file may have DivX5-compressed video with MP3 compressed audio, or uncompressed video with uncompressed audio, etc.
Anyway ... in practical terms, the codecs keep getting better and better, both as newer standards emerge (e.g., MPEG4 offers substantial advantages over MPEG2), and as the codecs grow in maturity (e.g., better and better motion estimation techniques) and add more and more features of the standards (e.g., DivX adding quarter pixel motion estimation [qpel] and B frames [um ... too hard to explain this late at night]).
So, in general, all other things being equal, you should use a newer codec (e.g., DivX5) over an older (e.g., Indeo). Of course, all generalizations are wrong.  There are other factors ... for video that you're going to edit more, consider using a lossless codec (e.g. HuffyUV) so that you don't lose quality each time you edit in new transitions, new features, etc., then only doing your last save is a lossless (oops, i meant lossy) codec.
If you're going to stream your video over the web, your hosting company may only support one standard (e.g., mine for journeyscrossing.org only will do Real).
If you want burn your video to DVD, you're eventually going to end up using MPEG2, whatever tool you use, because that's what DVD fundamentally uses. For Super Video CD, you'll again use MPEG2, for VideoCD MPEG1.
Wow, you caught me in a talkative ("type-ative"? ) mood. hth!
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| fccHandler |
| Posted: Mar 9 2003, 06:36 AM |
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Administrator n00b
Group: Moderators
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Great job, dude! 
I might add that Huffyuv is 100% lossless (when it doesn't have to convert the color space). MJPEG is always lossy, but with PicVideo at quality 19+ you'll hardly notice it.
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May the FOURCC be with you... |
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| phaeron |
| Posted: Mar 10 2003, 06:50 AM |
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Virtualdub Developer
Group: Administrator
Posts: 7773
Member No.: 61
Joined: 30-July 02
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Nitpick: While Huffyuv is indeed 100% lossless, "95% lossless" doesn't make any sense.
ASF is a container format like AVI. Its primary compression formats before Windows Media were the Microsoft MPEG-4 series, although in fact it could accommodate any codecs that AVI could use (mostly via vidtoasf).
I think RealVideo is H.261/H.263 derived, and it definitely uses block-based compression. No one knows that much about the current formats, though. The Real technology was far ahead of the pack in low-bandwidth video streaming for some time and probably would have gotten farther if the player didn't suck (a situation similar to VIVO), which unfortunately gave Microsoft time to catch up.
The general rule with compression is that however you compress makes it harder to edit. Nearly all codecs compress within frames, so the ability to edit within a frame (crop, resize) is very restricted and only possible with certain formats. However, not all codecs compress across frames, and those that don't are much more hospitable to frame-accurate editing, because the frames are self-contained and can be added, deleted, shuffled, etc. without problems.
Another rule is that truly lossless compression is never, ever constant bitrate (CBR) -- that is, there is no lossless compression algorithm that always compresses. Anyone who says they have such an algorithm is probably also auctioning off a bridge on eBay.
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| fccHandler |
| Posted: Mar 10 2003, 08:08 AM |
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Administrator n00b
Group: Moderators
Posts: 3961
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Joined: 13-September 02
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| QUOTE (phaeron @ Mar 10 2003, 02:50 AM) | | Nitpick: While Huffyuv is indeed 100% lossless, "95% lossless" doesn't make any sense. |
Well, considering that my captured files are about 300MB per minute, and I usually compress them to about 10MB per minute, the extra 5% can't really make much difference!
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May the FOURCC be with you... |
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| peewee |
| Posted: Mar 22 2003, 10:15 PM |
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Unregistered
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Thank you for the compression guide for dummies. 
I am a newbie also. I use virtualdub for video editing. When I compress a file it suggests I use MPEG4 compression. Where Where do I get a codec for Mpeg4? I don't want an editor program, just the compression program so I can get smaller files from virtualdub. The two maybe the same, and I don't know the difference. :/
Mark |
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| David.Bucci |
| Posted: Mar 23 2003, 02:10 AM |
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| QUOTE (peewee @ Mar 22 2003, 05:15 PM) | | Where do I get a codec for Mpeg4? |
DivX. Many people are saying you should stay with 5.02 rather than their newest version, 5.03, so I'd suggest you search around on their site for an archive of previous versions and use that.
There are other good ones ... newest Quicktime outputs MPEG4, I believe (but it's not free, and even if you have it you can't use it with VD), and there's a very active research project, Xvid, that may someday release a version that permits legal use ... right now, it's a testbed for trying out ideas, but doesn't pay required licensing fees to MPEG-LA, the body that owns the standard, and thus you can't use it for encoding of content (which is too bad, because it's quite possibly the most technologically superior codec on the planet!) |
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| fccHandler |
| Posted: Mar 23 2003, 03:38 AM |
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Administrator n00b
Group: Moderators
Posts: 3961
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| QUOTE (David.Bucci @ Mar 22 2003, 10:10 PM) | | newest Quicktime outputs MPEG4, I believe ... |
I encountered one of these for the first time just yesterday. I don't (and will not) have QuickTime, so I was looking for a way to extract the MPEG4 data into something I could view.
The file has an .mp4 extension, but internally it is an MOV container (like every other QT file I've seen). I tried to connect it to GraphEdit's "Quick Time Movie Parser" but it wouldn't connect. In the end I had to use a hex editor to fix some (apparently non-compliant) fields in the "hdlr" atoms. Finally I was able to do a direct mux of the audio and video streams into an AVI container.
The actual FOURCC of the .mp4 video is 'mp4v.' I tried every common AVI MPEG4 FOURCC I could think of but nothing would decode it. XviD is the closest thing to true MPEG4 that I know of, and since even XviD won't decode it, I'm questioning to what extent the QuickTime stream is truly MPEG4 compliant. Is 'mp4v' just another proprietary variation of the MPEG4 standard?
P.S. XviD won't decode DivX 5.03 either, though it does fine with 5.02 content.
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May the FOURCC be with you... |
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