Bitrate calculation problems due to VBR/CBR - please bear with me

[Chetwood]

Alright, by using the latest installment of DVD2SVCD I finally managed to leave these problems (http://forum.doom9.org/showthread.php?s=&threadid=24100) behind me and start encoding some Buffy eps for my little cousin as foolishly promised...

I'm aiming at one ep of roughly 42 mins per 800 MB CD with a special catch: I'm going to rip both english and german audio plus the same number of subtitles. Still 40 mins on one CD sounds like really good image quality, my problem however is that I do not know which average bitrage to select since I'm using both CBR (audio) and VBR (video).

So I tried the following calculation (I do not need any title picture or menu stuff):


SVCD = 2657 kbit/s max.

2657 kbit/s
./. 192 kbit/s audio english
./. 192 kbit/s audio german
./. x kbit/s subtitles english
./. x kbit/s subtitles german
---------------------------------
2273 kbit/s


Now I got 3 probs:

1. How much space (kbit/s) will the subtitles presumably consume?
2. How much safety margin do I subtract from the VBR bitrate of 2273 kbit/s?
3. Where do I enter the final bitrate in the bitrate tab of DVD2SVCD?

Should I go and set both min/max avg. bitrate to the same value? Or should I change the time value 'Between 0 and 42 min use 1 CD size 800' (0-2337) and use that value?

Using bitrate calc (http://www.vcdhelp.com) I tried

max: 2336
max avg. 2216
min avg. 2216

cause max. avg should be 120 kbit/s < max bitrate. Is this the way to go or could I squeeze out more? TIA!

[UltimateDBZ]

Quick question: You realize that unless you have permanent subtitles, the subs won't be visible on a DVD player, right? So unless you have a standalone SVCD player, it wouldn't make sense to have subs in 2 languages, as only 1 could be permanently visible (to my knowledge). Just making sure...

[pacohaas]

the whole idea of the bitrate tab is so you don't have to do all these calculations, just make sure you set up the desired cd size for each given time range and it will do it for you.

[Chetwood]

@UltimateDBZ

Thanks ;) But YES, I've read the FAQ (and remember my thread linked to above) so I know this. I've tried it on my standalone and works perfectly: I can switch between no, english and german subtitles as well as between english and german sound. I just want to make sure that I suqeeze as much as possible video quality out of it.

[Chetwood]

Originally posted by pacohaas
the whole idea of the bitrate tab is so you don't have to do all these calculations, just make sure you set up the desired cd size for each given time range and it will do it for you.

That's what I'd thought. I'm just wondering if the tool uses the maximum video bitrate at all times when the bitrate tab says '? - 1627' or something. I mean, there's got to be a reason why you can set the bitrate manually to an average maximum...

The problem with the CD's tab is that when I've set it to default and then selected:

'Between 0 and 43 mins use 1 CD size 800 = ?-2149'

I get the message

The total bitrate (audi+video=2914) is bigger than the max bitrate specified in the SVCD standard (2756).

How come? I think DVD2SVCD was supposed to choose the *remaining* video bitrate (the 2 audio streams are CBR) accordingly by itself?

[UltimateDBZ]

Originally posted by Chetwood
@UltimateDBZ

Thanks ;) But YES, I've read the FAQ (and remember my thread linked to above) so I know this. I've tried it on my standalone and works perfectly: I can switch between no, english and german subtitles as well as between english and german sound. I just want to make sure that I suqeeze as much as possible video quality out of it. Alright, just making sure you weren't wasting valuable bits on subs that wouldn't work ;)

[smiller667]

Originally posted by UltimateDBZ
Quick question: You realize that unless you have permanent subtitles, the subs won't be visible on a DVD player, right?Ummm ... not really. True, there is no software DVD player that will show selectable SVCD subs ... quite a few DVD standalones, on the other hand, will happily play back either CVD- or SVCD-style subtitles ...
Regarding the bitrate for subs: if you calculate at 50kbit per subtitle stream, you are probably on the safe side ... it should be taken into account by dvd2svcd, but I personally like to double-check ... in particular when using the I-Author muxer which is very critical regarding the max. total bitrate.

[ux-3]

DVD2SVCD will give you the highest possible bitrate, thats why audio and subtitles are done before video I guess. The bottom settings are basically to please your player, what good is a high bitrate, if it is too high for your player.

[Labersack]

I get the message

The total bitrate (audi+video=2914) is bigger than the max bitrate specified in the SVCD standard (2756).

How come? I think DVD2SVCD was supposed to choose the *remaining* video bitrate (the 2 audio streams are CBR) accordingly by itself?

If you use 2*192kb Audio streams, you should set your max. rate to 2756-2*192=2372, to stay in the specs. btw: If your movie is 40min or longer, DVD2SVCD will calculate a bitrate that is lower than 2756. The critical point for a CDR80 is at ~39:30, longer movies will have an avg lower then the specs, shorter movies will be 'violating' the specs, but most players will play them anyway.

If your player can handle higher bitrates, you can ignore this border. You will do a kind of 'XSVCD', but most player cand handle them. Best to try one movie on a CD-R and check. I set both max and maxavg most times to 2500 and I also do 2 languages und two subtitles. I always get the warning that max and maxavg are closer than 120kb, but because the calculeted avg will be lower (you can see the real used bitrate when CCE is started), there will be no problem in the CCE-stage.

[Chetwood]

I've down it now using the bitrate tab and setting the values to
42 mins and 740 MB so one Buffy ep fits on one CDR. However, I'm not too happy with the results cause I get a lot of artifacts when the camera is moving faster. I can't imagine that one additional audio track of 192 kbit is making that much of a difference.

IOW, I'm not quite sure if DVD2SVCD managed to assign the maximum video bitrate that it could have. Is there any way to check the birate by examining the 'bbMPEG_Muxed_File-subbed00.mpg' on the computer?

[Labersack]

Yes, there are several bitrateViewers.
But you also can check you logfile to see what rate is used.
Are these picture problems realy artefacts or maybe an interlacing-problem?

[Chetwood]

Originally posted by Labersack
Yes, there are several bitrateViewers.
But you also can check you logfile to see what rate is used.
Are these picture problems realy artefacts or maybe an interlacing-problem?

Do you have any urls for the bitrate viewers? I'm quite certain to say that it's not an interlace problem cause the 'normal' scenes in the movie do not show any artifacts. Besides, I don't get any on my computer when watching the mpg. These I DO get when watching the Family Guy mpegs I've encoded, cause the Famgy DVD quality is comparatively bad.

Well, I forgot to check the DVD2SVCD log so I'm gonna do it on my next encode. This time I'm gonna set the bitrate manually to see if there's a difference.

[Labersack]

Sorry, I don't know any URLs of a bitrate viewer.
There is an option to put some info on your SVCD. Maybe you have checked this option at your conversion. Verify if in your SVCD is a folder named 'extra' and if in this folder is an info-file. If yes, you can read some settings of your movie there, also the used bitrate.