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Thread: CVD:What is it,how to test it & what to expect!

1. 21st Jun 2002 10:55 #1
   SatStorm

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   The Old One

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   Join Date: Aug 2000

   Location: Hellas (Greece), E.U.

   

   

   CVD (China Video Disc): What is it, how to test it and what to expect!
   By SatStorm & VCDhelp Forum Members
   
   
   The History: What is CVD, SVCD (Super VCD) and Chaoji VCD
   
   As we all know, Super Video CD is an enhancement to Video CD, that was developed by a Chinese government-backed committee of manufacturers and researchers, on 1998. But SVCD, the way we know it today, was the final version of the second generation CD based movie media in China. The full story starts 2 years earlier, early 1997. That year, there were originally three independent efforts of bringing the next-generation video disc standard to the Chinese market:
   
   - China Video Disc (CVD), developed by C-Cube Microsystems and its Chinese OEM partners
   - Super Video CD (SVCD), developed by China Recording Standards Committee under the requirements given by Chinese Ministry of Information Industry, with technical support from ESS Technology
   - High-Quality Video CD (HQ-VCD), developed by the Video CD Consortium (consisting of Philips, Sony, Matsushita and JVC, the companies that created the original White Book Video CD specification)
   
   C-Cube with CVD, got a healthy head start, mostly because it was already an established subcontractor in the Chinese VCD player market. The development of the CVD specification began in 1997 and the first CVD players were released on the market in June 1998, while SVCD and HQ-VCD specifications were still at a draft stage.
   This move apparently created some panic in the SVCD and HQ-VCD camps, and the result was that the Chinese government, agreed to back the creators of the rivalling HQ-VCD specification. The overall deal was actually a big win to the Video CD Consortium (i.e. Philips-Sony-Matsushita-JVC) since they were late players in this game to begin with.
   However, most of the big VCD player manufacturers in China were backing C-Cube's CVD standard, and there were already approximately 300 000 to 600 000 CVD players in the distribution channels. To resolve this problem, the Department of Science and Technology of Ministry of Information Industry forced a compromise in incorporating CVD and SVCD under a single umbrella format called "Chaoji Video CD" in November 1998.
   So, "Chaoji VCD" (which roughly translates to 'Super VCD') is not actually a new disc format, but more like a compatibility specification for players. A Chaoji VCD player must be able to play back at least SVCD, CVD, VCD 2.0, VCD 1.1 and CD-DA discs.
   Today, all PAL standalone DVD players, when they state "SVCD compatible", are actually compatible with Chaoji VCD players. That means that both CVD and SVCD formats are supported.
   
   Update: The DVD players for USA (NTSC, Region 1), are not forced to include CVD compatibility when they state SCVD compatibility. The reason is simply: Those standalones are not for use in China, even in theory (as happens with R2 PAL ones...).
   After lot of reports, looks like only the half of the DVD R1 standalones, reported compatible with SVCD, are also compatible with CVD. That makes it about 40% of the total R1 DVD Standalones. Most of them are made in southeast asia, and they using C-Cube's microchips.
   
   More (but a lot outdated) infos for CVD/SVCD in General you can read at the following Link: www.uwasa.fi/~f76998/video/svcd/overview
   
   
   Technical features of CVD
   
   In terms of video and audio quality, China Video Disc (CVD) is in between VCD 2.0 and DVD. It is using variable bitrate (VBR) MPEG-2 video up to 2.6 Mbps and either 1 or 2 MPEG-2 Layer II stereo audio streams). It is also possible to use MPEG-2 Multi-Channel 5.1 surround audio, but there are no many players out there to support this feature. Philips players reported that are compatible. For your information, the easiest way to produce multi channel audio CVDs,/SVCDs is through Linux. That makes the creation of such discs a very difficult task. So, it is not surprising that only demos of this feature exist today...
   
   Update: The new versions of the great Fronter DVD2SVCD, supports the easy creation of MPEG-2 Multi-Channel 5.1. The first tests from users, reports that lots of DVD standalones, decodes the audio as typical stereo. Further Testing is neccessary, and short reports from users/testers are welcome!
   
   Switchable subtitling also supported. In the matter of fact, CVD's switchable subtitling was adapted "as it is" from the SVCD format (except Philips players, as usual). With the well known Chinese program "I-Author" (you can find a demo in the VCDhelp.com utilities page), which was optimised for CVD authoring/creation, video enthusiast find ways to add subtitles to their SVCDs. That wouldn't be possible if SVCD wasn't full compatible with CVD. Today, there are other alternatives to add subtitles to SVCDs/VCDs, but I-Author continues to be the best solution (more compatible) for this. The bad news, is that there is no way to buy the program outside China. Thank God, Internet has no borders!
   Finally, CVD, like SVCD, supports HTML style hyperlinks, still images, playlists/slideshows, multi-level hierarchical menus and chapters (indexing). To make that even more clear, for many things, SVCD is CVD compatible and not the opposite. CVD set once some standards, and SVCD adapt them!
   The CVD picture resolution is 352 X 576 for Pal and 352 X 480 for NTSC. This resolution has a name: 1/2 D1 (some call it D2). It is also a legal DVD - Video resolution.
   
   
   Why to choose to encode to CVD and not SVCD.
   
   CVD has all the efforts of the well known SVCD, but with 1/2 D1 resolution (some call this resolution D2).
   This 1/2 D1 (352 X 576/480), happens to be a legal resolution for DVD - Video also. So, you can use your 352 X 576/480 mpeg 2 files on CDs today and on DVD -/+ R(W) tomorrow, without any picture re-encoding or re-scaling. This is not possible with SVCD, 'cause the resolution used by this format (480 X 576/480), ain't compatible with DVD - Video. So, SVCD files needs re-encoding if you want to burn them on DVD. There are (of course!) ways to convert SVCDs to DVD-Rs without re-encoding, but that creates something like "xDVD" and many players does not support discs with such files. The most common problem, is a picture with totally wrong aspect, or blank picture in the right of TV screen!
   With CVD you don't have that kind of problems, plus ALL your DVD authoring programs gonna accept your CVD files as 1/2D1 - DVD ones! So, it is more easy to author files and create menus, etc.
   
   The resolution of 352 X 576/480 also happens to be the official SVHS resolution. So, grabbing at this resolution from a SVHS source and direct encoding it to CVD, make the conversion almost lossless with the use of standard CVD/SVCD bitrates (~2520kb/s).
   The "S-Video in" connection, most capture cards today includes, is also (in practice) limited to this resolution. S-Video can give very high resolutions, but it is almost impossible to use a resolution beyond 352 X 576/480 with SVHS. (The true varies a little and it is ~384 X 520 for both PAL/NTSC, but ain't noticeable anyway)
   
   Update
   Now, it is a perfect opportunity to clarify a myth here: There is no way to grabb from any analogue source (including TV broadcasts) and with the use of "S-Video in" to get a usefull resolution beyond 384 X 576/480.
   The reason for this, is that in analogue technology, there are no horizontal lines like the digital world, but horizontal DOTS. 720 dots in a raw, creates what we call a line. With the analogue transmissions, if a dot is missing in the raw, there gonna be no replacement, just a null dot, a nothing. The lenght of the raw, gonna be always the same with or not some dots. For example:
   
   A line with all the dots: .................................................. .........
   A line with some dots missing : ... ............. ............. ..................... ...
   
   In theory all types of connections/cables are capable to carry a picture of CCIR-601 resolution from a source to a screen, but there gonna be loses in the dot raw line like those in the example. Those loses are more for composite, less for S-Video and even less for Component and RGB. It is not easy to expain it further in a simply post, maybe a future article
   With S-Video, those loses are about 1/5 of the video in theory. In practice and mainstream cables/connectors, is more, about 2/5 or the original info.
   So you end up with 384 horizontal usefull dots X 576/480 vertical lines. And becase in digital world only the usefull info counts, any grabb with the use of S-Video beyond 384 X 576/480 is a fake!
   If you want source on higher resolutions, you can experiment with DV, DVB transmissions (when you grabb direct the stream with the use of special hardware), DVD - Video (ripping) and source which came from Component adaptors or RGB ones. The full Euroconnector cable (known more as SCART) includes sometimes the RGB info, but a Full SCART to SCART cable required , with high quality parts and those cables costs a lot!. Also, the difference ain't easy noticable on a TV, but is very noticable from the encoders!
   Overall, don't expect higher resolutions beyond 384 X 576/480 with the use of S-Video! It is practicly impossible to have them! And because 384 X 576/480 ain't a supported resolution in any optical media, go straight for 352 X 576/480. And guess what, that is the resolution of CVD!
   
   Back to our subject: It is true that using Cinemacraft encoder and the maximum possible CVD bitrate (2520kb/s if you use audio 224kb/s), any CVD from a SVHS (S-Video) source looks identical with the original source.
   With the new TMPGenc Pro, and the use of the new 2 Pass VBR mode, almost the same quality is possible (not that good but close enough), but that requires advance knowledge of TMPGenc settings which is not the easiest task for most users. You need to test a lot with this encoder to find the correct way to succeed that kind of quality! There is no "load template, hit encode" solutions with TMPGenc! Always remember that!
   
   Another reason to choose CVD and not SVCD, is the picture quality issue in general. CVD is always overall better.
   - If you are a quality freak, then the CVD format is a better choice than SVCD. CVDs can use the same bitrates as SVCDs but for a lower Horizontal resolution. So, the data shared to each field/frame is more for CVD, than the data shared to each field/frame for SVCD. That is the secret: More data per frame, at the same bitrate, better picture for CVD.
   Just for your information, the less horizontal lines ain't noticeable in a average TV of any screen size. Only if you own a HDTV, you might see CVDs a little bit more blurred than a SVCD. You can prevent this, if you use wise a sharpen edge filter during the encoding. With TMPGenc, try values like 8/16/32/64. That sharps the picture, the same way we sharp any picture on our VCRs.
   - If you belong to the "more per CD" party, then CVD is also the way to go: With CVD you get SVCD picture quality, with lower bitrates. That means smaller files.
   
   Some Examples to play with:
   
   # A CVD with a CBR bitrate of 2520kb/s looks better (less blocks/smoothness) than a SVCD with a CBR bitrate of 2520kb/s
   # A CVD with a CBR bitrate of 2350kb/s is picture quality equal with a SVCD with a CBR bitrate of 2520kb/s
   # A CVD with a VBR bitrate of 1200kb/s minimum, 2300kb/s average, 2520kb/s maximum is equal a SVCD with a VBR bitrate of 1200kb/s minimum, 2520kb/s average, 2520kb/s maximum. In theory, this settings produce the best SVCD quality possible, even if average/maximum have the same value, 'cause picture is scanned twice and a better allocation of data per frame succeeded.
   
   
   Update Ain't SVCD better in picture, because of the more resolution (480 horizontal lines)?
   
   Well, yes and no. The 128 horizontal lines ain't that important for picture quality. The difference between a CVD and SVCD ain't noticable to mainstream television sets, only enchanced and HDTV ones. In other words, for the 80% of the TV sets out there, there is no real differance. For the lucky owners of the rest 20%, yes it is. A slighty one, but it is! SVCD is sharper!
   There is a way to to eliminate this :Use sharpn filters when you encode.
   With TMPGenc plus for example, if you use the sharpen edge filter and the values 8/16/24/32 , you eliminate any difference in sharpness between CVD and SVCD. But use those filters wise, 'cause from a point and beyond, filters add noise to your ouput files!
   Of course, you can use this tip with SVCDs too, and get even better sharpness with them, but this is another point...
   
   The Vertical lines are the ones that counts for real. Those are the ones which give detail and crystal clear picture to our encodings.
   Also, because of the Less Picture resolution of CVD but the same possible maximum bitrate as with SVCD, CVD is more flexible and give us more choices:
   We can use standard SVCD bitrates and get better picture with CVD (more data per frame that way than SVCD), or use lower bitrates and get equal picture with SVCD (With CVD's resolution, less pixels needed per frame than SVCD to produce equal picture).
   Overall, with CVD, we can choose: DVD near picture quality or SVCD picture quality but with much more video per CD.
   
   "Shocking": CVD is DVD-near quality!
   
   For quality freaks I suggest CVDs with Constant Bit Rate (CBR) up to 2520kb/s. With this bitrate, you get 35-38 min per CD, and it is near DVD quality.
   That is a technical true: A CCIR-601 DVD-video file, uses an average bitrate up to 5000kb/sec.
   A 1/2D1 DVD-Video, needs an average bit rate up to 2.500 to produce the same quality but for the half resolution. Simply mathematics?
   The CVD maximum bitrate is 2520, like SVCD. That means that it is possible to use the same bitrate as with 1/2D1 DVD-Video files. Now, I remind you that CVD has the same resolution (352 X 576/480) with the 1/2D1 DVD video. So, if you compare them, the only differences between a CVD file with 2520kb/s bitrate and a 1/2D1 DVD-video, are the multiplexing and the maximum possible bitrate. With CVD that is limited up to 2820kb/s (if you don't use audio), while with DVD you can set it up to 9000kb/s. The resolution is the same and, the Average bitrate can be the same.
   From this point, CVD is for real "DVD" near quality. Well, 1/2D1 DVD-Video near quality... But we can still say DVD-near quality, won't we? Who gonna notice a small "1/2 D1" before the "DVD"?
   
   Suggested settings for CVD:
   
   - For ultra quality freaks, I suggest 2 Pass VBR with 1200 minimum/2520 average /2520 maximum. Better allocation of data per frame can be expected from this, but to tell you the true, ain't worth the time!
   - Top quality can be expected with CBR up to 2520kb/s. You get 35-38 min per CD, and it is near DVD quality. I also suggest:
   - For 4:3 movies, I suggest 2 Pass VBR with 1200 minimum/ 2350 average / 2520 maximum.
   - For 16:9 movies, I suggest 2 Pass VBR with 1200 minimum/2150 average/ 2520 maximum.
   - For 2:11:1 movies, I suggest 2 Pass VBR with 1200 minimum/1900 average/ 2520 maximum.
   
   Those settings produce top quality at fair filesize. You can set higher bitrates and get better pictrure, or set it lower and get smaller files (more per cd that way). You have to test yourself a lot and find what is suitable for your needs, if the suggested ain't look good enough in quality for you.
   I don't suggest CQ modes, 'cause I don't like them. If you are a fan of CQ modes, do your own tests. In generall, I can only say that CQ_VBR @ 3000 maximum/1200 minimum and 65%, gonna produce files like the ones with the 2350 average, but in much bigger files.
   
   In case someone interest on what I use when I encode to CVD:
   Personally, for 4:3 movies, I prefer to use 2 Pass VBR with 1200minimum/1900 average/2520 maximum and I really like the picture. For most movies, those settings give me amazing results ("Matrix" for example). There are exceptions of course (example: "Mummy returns", don't try to set the bit rate less 2450kb/s), but there are limited.
   For movies with 16:9 aspect, I prefer to use 2 Pass VBR with 1750kb/s average. With 2:11:1 aspect source (very common for current music videoclips and a lot of current movies grabbed from DVB transmissions), most of the times 1450kb/s average is enough! There times I set it even lower (1250) and still get excellent results! An example, just for the record: I just finished encoding the movie "Highlander 4: Endgame", which is 93 min. The source was a DVB transmission with 2.11.1 video aspect (almost half vertical 4:3). I encode it to CVD with the shocking average bitrate of 1100kb/s Video + 160kb/s Audio. The whole movie fit on one cd, and the picture quality is excellent! Amazing! I couldn't believe my eyes! That is logical in a way: The active window of this movie is 352 X 320 lines (~ 2.11.1) The rest of the picture are black borders in the whole 352 X 576 final mpeg 2 file. So, you can use VCD bitrates, because you have to feed with data only the active screen. In a way, it is like Picture in Picture. Remember that 352 X 320 is fair close to 352 X 288 of the VCD resolution. If you see it in general, it is simply mathematics! I report that only as an example for advanced users, just to show the possibilities.
   I also fit on a CD the whole 123min "Mummy returns" movie, using 352 X 288 (2.11.1 source aspect) @ average 690kb/s (!) and believe it or not with almost no macroblocks! Unfortunately, I can watch it only on PC, 'cause that low bitrate ain't acceptable from my DVD player
   
   But again, all those settings looks good for me. Most of the users out there wouldn't go lower 1900 kb/s average! I can't blame them, if you have a DVD burner, there is no real reason to low the bitrate that much...
   Only if you want to do it for the fun..
   
   
   The Audio Issue
   
   CVD and SVCD use the same audio characteristics: 1 or 2 MPEG-2 Layer II stereo audio streams and, unfortunately, sample rate 44100Khz like audio CDs. That makes the audio incompatible with DVD. The audio must be 48000khz to be compatible with DVD.
   That means re-encoding if your audio source comes from CVD/SVCD and even if it is fast (so some could say ain't big deal), the upsampling ain't lossless!
   There is an alternative, if you don't like that wastin