DVD vs SVCD profile / bitrate matrices

[denali]

Hello all,

I've been a registered user of SVCD2DVD since '06 and it's testament to the quality of the program that this is the first time I've needed to seek help. Apologies if this is discussed elsewhere; I've tried searching through the forums but quoted search strings are temporarily blocked which is making it hard to narrow down my searches.

I'm also aware that technically this post could be seen as advocating warez and thus fall foul of the forum policy, however it's difficult to explain the issue without some context so here goes.

My main use for SVCD2DVD is to convert a small number of UK PAL TV shows to NTSC DVD for sending to friends living in NTSC territories. Historically I've sourced these programmes from a Series 1 TiVo, which is an analogue source PVR with its own MPEG encoder. Because TiVo does its own encoding the bitrate of the source material is high, and consistent, regardless of the broadcast quality and has meant that SVCD2DVD has until now always used the DVD Profile when creating Title Sets. The results have generally been excellent.

More recently I've started using a Topfield TF5800 Freeview PVR as the primary source, and have run into a slight problem. Some of the programmes I'm trying to encode are from a channel with a high bitrate (6500+kbps) while others use a lower bitrate (3100-3500kbps-ish). When playing the original MPEGs back on a 32" LCD it's quite difficult to tell them apart, but it's a different story with SVCD2DVD.

SVCD2DVD converts the 6000+kbps videos to NTSC using the DVD Profile, and the results are gorgeous. However for the 3000+kbps videos it insists on using the SVCD Profile and Low Bitrate Matrices. This produces a very noticeable drop in quality when the final DVDs are played back on a stand-alone player, even though there is less footage on the lower quality disc (3x45 minute episodes vs 3x50 minute episodes).

Obviously SVCD2DVD is choosing the Profile and Bitrate based on the bitrate of the source material, but I wonder if it isn't being a bit aggressive with what it considers low. Is there any way of forcing it to use the DVD Profile and higher bitrate matrices, and do you think there would be any quality improvement in doing so?

At the moment I am using 2-pass encoding for the lower bitrate material (the higher rate stuff is so good it doesn't really need it). Is that the best I'm going to get? It's a little disappointing given the finished product quality I'm used to, but I guess if the source bitrate is halved there's really not much to work with.

For what it's worth the source resolutions are 704x576 in both cases, so should not be a factor.

Any info or advice would be appreciated.

Thanks.

[denali]

SVCD2DVD converts the 6000+kbps videos to NTSC using the DVD Profile, and the results are gorgeous. However for the 3000+kbps videos it insists on using the SVCD Profile and Low Bitrate Matrices. This produces a very noticeable drop in quality when the final DVDs are played back on a stand-alone player, even though there is less footage on the lower quality disc (3x45 minute episodes vs 3x50 minute episodes).

Obviously SVCD2DVD is choosing the Profile and Bitrate based on the bitrate of the source material, but I wonder if it isn't being a bit aggressive with what it considers low. Is there any way of forcing it to use the DVD Profile and higher bitrate matrices, and do you think there would be any quality improvement in doing so?

I've just checked the properties of the temporary "_S2D.mpg" files created in each instance, and for the DVD Profile conversions the resolution is 720x480, while for the SVCD Profile files it is 480x480. Bitrates notwithstanding I am clearly losing 33% of my horizontal resolution, which explains the poor quality results cf the original MPEG.

This is beginning to look less like a feature and more like a bug. Could SVCD2DVD be misinterpreting the source of the video as being SVCD? If so, is there any way to force it to see it otherwise?

Thanks.

[Jikchung]

Can you post logs from these runs (one that yield DVD, one that uses SVCD resolution and low-bitrate matrices)? Source bitrate alone will not be the determining factor for output resolution.

[denali]

Can you post logs from these runs (one that yield DVD, one that uses SVCD resolution and low-bitrate matrices)? Source bitrate alone will not be the determining factor for output resolution.

I'll post some logs later when I have a chance to sort through them, but in the mean time I have a confession: as well as the lower bitrate I've re-checked the resolutions of the two sources and the higher quality one is indeed 720x576 but the lower quality one is actually 704x576. I don't know how I had them down as being the same when I posted my first message, but I had so many media players and encoders running it's quite possible I just read the wrong figures.

If I use DVD Patcher to hack the resolution of the 704x576 file to 720x576, SVCD2DVD renders it with the higher quality matrices (albeit with a blank area on the right of the screen, obviously). So, in this case at least, resolution seems to be the deciding factor.

As I understand it 704x576 is an acceptable resolution for PAL DVD so I see no reason why SVCD2DVD can't deal with it as is, unless it is the NTSC conversion routines themselves that insist on a minimum of 720x576.

I can always re-render these lower resolution files into 720x576 using a third-party application but I was really hoping to avoid unnecessary complications (and delays!). If it's not possible to force SVCD2DVD to use the higher built-in matrices, might a custom matrix help? It's a feature I've successfully avoided until now (it looks way too complicated) but it's a route I'm prepared to take if it helps to avoid third-party re-rendering.

Thanks for the feedback.

[Jikchung]

My understanding on matrix use is that the 'low-bitrate matrix' is used when the final result of the encode will be below a certain bitrate level (due to duration of source file). The logs will be valuable in seeing what's actually happening.

Regarding matrices, have you read this sticky?
https://forum.videohelp.com/viewtopic.php?t=282219

[denali]

My understanding on matrix use is that the 'low-bitrate matrix' is used when the final result of the encode will be below a certain bitrate level (due to duration of source file). The logs will be valuable in seeing what's actually happening.

I've just run a test project with one VTS containing a high-bitrate source file, and a second VTS containing the lower-bitrate source file. As expected SVCD2DVD has rendered the first using the DVD profile and the second using the SVCD profile.

The log for this session is attached.

Regarding matrices, have you read this sticky?
https://forum.videohelp.com/viewtopic.php?t=282219

I have looked at that but it means very little to me. I could start wading through the attached custom matrices one by one and see what happens, but without even knowing what the matrices are or how they related to encoding it would be shooting in the dark.

Thanks.

svcd2dvdlog-20070421200819.txt

[denali]

My understanding on matrix use is that the 'low-bitrate matrix' is used when the final result of the encode will be below a certain bitrate level (due to duration of source file). The logs will be valuable in seeing what's actually happening.

I've just run a test project with one VTS containing a high-bitrate source file, and a second VTS containing the lower-bitrate source file. As expected SVCD2DVD has rendered the first using the DVD profile and the second using the SVCD profile.

The log for this session is attached.

Regarding matrices, have you read this sticky?
https://forum.videohelp.com/viewtopic.php?t=282219

I have looked at that but it means very little to me. I could start wading through the attached custom matrices one by one and see what happens, but without even knowing what the matrices are or how they related to encoding it would be shooting in the dark.

FWIW this morning I tried using SVCD2DVD to re-encode the awkward file using two sets of custom matrices extracted using VideoReDo, the first extracted from the 704x576 file itself and the second extracted from the 720x576 file. In both cases SVCD2DVD still used the SVCD Profile. From this I'm concluding that SVCD2DVD's decision as to which profile to use is completely independent of the choice of matrix.

Which brings me back to the source of my original confusion: how does SVCD2DVD determine what constitutes a DVD quality file as opposed to an SVCD quality file when it comes to PAL-NTSC conversion? I see three main possibiliites:

1. Decision based on source resolution i.e. 704x576 sources will always be converted at the lower quality regardless of bitrate. Disappointing if true, because 704x576 is a perfectly standard DVD resolution

2. Decision based on bitrate i.e. anything in the region of 3-3.5kbps will be considered SVCD-only.

3. Decision based on an internal calculation dependent upon both resolution and bitrate.

In any case, my original question stands: is there any way to goad the program into using the DVD Profile for any given file regardless of parameters? I realise that due to the way compression and NTSC conversion works this could result in an output with even worse quality loss, but I'd really like the opportunity to give it a try.

There are still a few avenues to try and find my own solution to this, but I've already wasted hours this weekend rendering, converting and re-rendering the same files under slightly different conditions and I can't believe that nobody has seen this behaviour before.

[Jikchung]

OK, I see what you are talking about. My understanding of how/why matrices are called may be flawed. At any rate, we will need to wait for ChrissyBoy to get back to us on this one, the log should be enough for now.

It's probable that we have all seen this behavior, but had good results and no need to evaluate further.

[denali]

OK, I see what you are talking about. My understanding of how/why matrices are called may be flawed. At any rate, we will need to wait for ChrissyBoy to get back to us on this one, the log should be enough for now.

It's probable that we have all seen this behavior, but had good results and no need to evaluate further.

I've done a little more playing and the use of Profile is definitely down to the source resolution. I used DVD Patcher to hack one of the 'good' files to 704x576 and SVCD2DVD tried to use the SVCD Profile to convert even though the bitrate was still high.

The good news (for me at least) is that this experiment led me to a workaround:

• 1. Use DVD Patcher to hack the 704x576 file header to 720x576.
  
  2. Load the hacked file into SVCD2DVD as an Asset, and add it to a VTS.
  
  3. Hack the file back to 704x576.
  
  4. Create DVD.

The result is beautiful, and virtually indistinguishable from results achieved with the higher bitrate, higher resolution sources. Just to confirm I checked the converted file's properties with Media Player Classic, and the final DVD's properties with IFOEdit, and everything seemed to be in order with no odd resolution or format mixtures like I was half expecting there to be.

Thus far I've only tried this with a single source file. The ultimate proof will be when I've done a three-episode disc, shrunk it to DVD5 with DVD Shrink, and shoved it on the stand-alone player. I can't imagine there'll be any problems, though.

The bottom line in all this, though, is that under certain circumstances when converting from PAL to NTSC SVCD2DVD seems happy to throw away information from perfectly good DVD compliant files and render them down to 480x480. Might I be so bold as to suggest one of the following:

• 1. Tweak the program such that 704x576 PAL assets are rendered as DVD not SVCD or
  
  2. Add a "Use DVD Profile for all Assets" option to the Preferences.

I'd guess the latter would be easier?

Thanks.

[ChrissyBoy]

Might I be so bold as to suggest one of the following:


1. Tweak the program such that 704x576 PAL assets are rendered as DVD not SVCD or

I have a build which will do this. Would you like to drop me an email & you can give it a whirl...