SVCD quality CBR vs VBR

[mmx]

Apologize if this have been brought up many times. I scan the forum but have not found an answer to this:

Using tmpgenc, for SVCD for DV, if I use CBR of 2520 versus VBR (2-pass with max 2520 and average 2000), I would expect to have better quality using CBR, right?

I understand that file size will be bigger with CBR but each frame is getting the max bits. With VBR, the max is still limited at 2520.

Thanks

[bugster]

If you want to fairly compare CBR Vs VBR, you should use the VBR Average figure Vs the CBR figure.

So CBR 2500 SHOULD be better than VBR 2000. That of course assumesall other things being equal and the material actually needing the extra bitrate (not just a still picture or talking head type of scene).

[RabidDog]

Using the example you gave, yes CBR will give better quality. Simply becuase every frame gets the maximum allowed bitrate whereas in vbr @ avg 2000 some frames might be slightly starved of bits... I doubt in practice you would notice a great deal of difference, unless there was a lot of fast action or the source was noisy(grainy).

[jimmalenko]

You are correct.

[hyena77]

so if file size is not an issue, would CBR always be better than VBR?? cuz thru all my readings on this forum, i was led to believe that VBR provided the best quality out of all the types of bitrates for encoding and this topic has me all confused

[bugster]

so if file size is not an issue, would CBR always be better than VBR?? cuz thru all my readings on this forum, i was led to believe that VBR provided the best quality out of all the types of bitrates for encoding and this topic has me all confused

For SVCD, Max video bitrate is 2520Kbps (I believe, but lets assume that anyway).

CBR 2520Kbps Vs VBR with an Average of 2520, Max 2520, will be pretty much identical.

CBR 250Kbps Vs VBR Avg 2000, Max 2520, CBR SHOULD have a slight edge in quality, but to a certain extent it depends on the source material and the amount of action involved in the movie.

Basically. If you want to be sure of the best possible quality and are not botthered about playing time, stick with CBR.

[hyena77]

i currently have a video where if i use CBR, the vid bitrate is 2184. if i use VBR, i have max 2520, avg 2184 and min 2000. should i still stick to CBR?

in what situations would you use VBR over CBR?

[bugster]

i currently have a video where if i use CBR, the vid bitrate is 2184. if i use VBR, i have max 2520, avg 2184 and min 2000. should i still stick to CBR?

in what situations would you use VBR over CBR?

So in that case filesize IS an issue. So use VBR.

[RabidDog]

IN your situation the only reason NOT to use vbr is that it takes twice as long as CBR. The only real reason to use CBR is when your clip will fit onto your media at the full bitrate.. or you value computer time more than video quality.

[jimmalenko]

@hyena77:
I will use a 120 minute film as my example. Sorry for the novel !

You have to make a decision regarding size output. If you do not have any size constraints, you can specify any bitrate you want and therefore CBR is the best way to go because all frames are getting the maximum bitrate and therefore present maximum quality. If doing a SVCD, you can set it at a max of 2520 CBR to get the best possible output. You will only get 35min to a CDR though. This will require 4 CDs with the last one only using about half a CD (3 x 35 + 15 = 120mins).
However, if you want the movie to fit on say, 3 cds, you need to either use a CBR of 2197 or VBR with MAX 2520, AVE 2197, MIN 1800 or thereabouts.

The benefit of using VBR in this case is that high motion scenes have 2520 kbits at their disposal as opposed to 2197 and at the other end of the scale, black screens will only use 1800 kbits instead of 2197. At the end of the day the average across all frames will be 2197 and this is how it achieves the same filesize as 2197 CBR. So you can save space on scenes that do not need much bitrate and reinvest this into scenes that do need it which results in a better quality overall.

[ZippyP.]

i currently have a video where if i use CBR, the vid bitrate is 2184. if i use VBR, i have max 2520, avg 2184 and min 2000. should i still stick to CBR?

in what situations would you use VBR over CBR?

The point where you would choose CBR or VBR is strictly personal choice. Things that can affect your choice:
Some people have higher standards than others.
Quality of the source, crap in = crap out.
Quality of your TV or other viewing screen. Big screens show everything.

In your example I would use VBR. You need to do some encoding and decide for yourself at what bitrate you will choose VBR or CBR. Cd's are cheap but I like to have as few disks as possible. I almost always use 2-pass VBR and I encode overnight.

BTW, Your minimum should be as close to zero as possible and the maximum should be the highest possible. Don't restrict the encoder, give it as much room as possible to properly use the bitrate. For minimum I use 250 because my DVD player freezes when the bitrate gets too low.

[ronnylov]

@hyena77:
I will use a 120 minute film as my example. Sorry for the novel !

You have to make a decision regarding size output. If you do not have any size constraints, you can specify any bitrate you want and therefore CBR is the best way to go because all frames are getting the maximum bitrate and therefore present maximum quality. If doing a SVCD, you can set it at a max of 2520 CBR to get the best possible output. You will only get 35min to a CDR though. This will require 4 CDs with the last one only using about half a CD (3 x 35 + 15 = 120mins).
However, if you want the movie to fit on say, 3 cds, you need to either use a CBR of 2197 or VBR with MAX 2520, AVE 2197, MIN 1800 or thereabouts.

The benefit of using VBR in this case is that high motion scenes have 2520 kbits at their disposal as opposed to 2197 and at the other end of the scale, black screens will only use 1800 kbits instead of 2197. At the end of the day the average across all frames will be 2197 and this is how it achieves the same filesize as 2197 CBR. So you can save space on scenes that do not need much bitrate and reinvest this into scenes that do need it which results in a better quality overall.

If you use 80 minutes/700 MB CD-R then you will fit 40 minutes of SVCD video at max bitrate because the SVCD specification is made to allow 2X speed CD-drives to play the discs (and a 80 min disc played at 2X speed will play in 40 minutes). You can fit 800 MB of video on a 80 min CD-R as SVCD because SVCD use less error correction than data CD. So in your example it is still possible to fit a 120 min film on 3 discs at maximum SVCD bitrate if you use 80 min/700 MB discs. But it is also possible to fit the 120 min film on 2 discs using a lower bitrate and VBR but the quality will be much lower. I suggest using FitCD as SVCD bitrate calculator. The bitrate 2521 kbit/s maximum is when you use 224 kbit/s audio. But if you lower audio bitrate to 192 kbit/s (and then use mono audio) then the maximum video bitrate becomes 2553 kbit/s according to FitCD. Some DVD players can play higher bitrates than standard because the CD-drive is faster than 2X speed and then it may be possible to use higher maximum bitrates but then the disc is not SVCD anymore, it will be XSVCD - a non standard format.

[RabidDog]

yes if using 2pass vbr then setting the low bitrate to 250/300 is a very good idea. This means that the encoder has a much bigger bit bucket to blast blocky bits. eg settings low 250/avg 2000/hi 2520
incidentally its the avg rate that determins how much video will fit per CD, also how good overall the finsihed product will look. IMHO anything less than avg of 1600 is not acceptable and 1600-1900 is ok above 1900 will be quite good. IF your player will accept it then exceeding the upper limit say to 3000 or 3500 will give excellent results also, but makes your svcd non-standard.

[ZippyP.]

If my bitrate drops below 1700 then I switch to 352x480 resolution (CVD).

[xtreemkareem]

I'd go CVD all the way. It usually works and hey - I never notice the resolution issue on my tiny 19" TV. What I notice is lack of enough bits per pixel.... CVD lets you split up most movies onto 2 CDs with very decent quality.

[ZippyP.]

CVD lets you split up most movies onto 2 CDs with very decent quality.

I agree with you there.

[RabidDog]

CVD = half D1 .. a valid dvd resolution.. ergo will work in DVD authoring packages.

However if you burn as a DVD @ 356x576 then you lose the extra space of mode2.. the eternal dilemna