What is the difference between Variable & Constant Bit R

[ChachiFace]

Is there a difference in quality or anything else by choosing between Variable and Constant Bit Rate? (ex. Variable 7000kbps avg. 8000kps max. vs Constant 7500kps)

I noticed this setting using Ulead VS7, it's one of the compression options under video settins/video data rate.

Can someone please explain the difference to me?

Thanks,

ChachiFace

[snowmoon]

Huge difference...

Variable only uses as many bits as necessary to reach a specified quality level...

Constant bitrate uses as many bits as you give it all the time.


Bit for bit the VBR will produce better quality at a smaller file size because the full 8mbps is hardly needed all the time.

[dcsos]

I would say
If you can encode at 8 million bits..don't do VBR
vbr is only a way to put more than an hour on a disc...
If you want the best quality (not quite hi def) I would say keep your project to an hour per disc (they're cheap)
SNOW MOON....
I was told by
SONIC SOLUTIONS TECH support to always use CONSTANT BIT RATE
unless I couldn't fit the project on the DVD..

I was told this was to avoid the poorer quality of VBR encodeing..
Am I misguided by the DVD techs at sonic?

ONCE YOU KNOW YOU CAN"T FIT it at 8 MILLION BIT..
that's when higher quality comes from VBR


Sonic says to me if you use vbr when you coulda used cbr you might have worse results...make sense?

[Vejita-sama]

https://www.videohelp.com/forum/viewtopic.php?t=157572&highlight=variable+bitrate+constant

https://www.videohelp.com/forum/viewtopic.php?t=149413&highlight=variable+bitrate+constant

[BJ_M]

try the multipass CBR in CCE @ 7000-8500 3 pass .. nice results (if you have the room)


btw -- CBR doesnt mean that the bit rate stays EXACTLY constant.. it means that the buffer is kept constant .. if you look at a vbr or cbr encoded file with a bit rate viewer -- both will have variations in the bit rate - though more so with vbr (ussually - on avg source material) ..

CBR decodes better on some hardware decoders than does VBR - though it makes no diff. with software decoding .. the diff. though is almost not noticable (unless you are one of those that can hear a diff. using a $1500 AC Cord vs. a $8 AC cord on your power amp) ..

just for interest (i wasnt making it up) ..

http://www.graniteaudio.com/cable/page7.html <-- $1500 ac power cable
http://www.mitcables.com/products/products.asp <--- $2600 power cable

[snowmoon]

I don't think DVD writers or discs are cheap, so I tent to push the envelope. Also what's point of waisting bits. If I can't tell the difference on a 42" progressive scan TV then I doubt throwing more bits at it is a good idea.

[poopyhead]

dcsos,

not every scene in a DVD requires 8 mbit/s bitrate or whatever is set at the max bitrate....do you think a completely black scene transition really needs 8 mbit/s????

why not let VBR do it's job???

i.e. if a 500 MB file of the same video clip was encoded with CBR vs. VBR.....VBR will look better...y not encode the black scene transition at 2mbit/s (which is prolly more than it needs already)..and spread the remaining 6 mbit/s to other scenes that need more....

[dcsos]

I'm with you poopyhead..Most of us do have to get over an hour on these discs!
Because I spent over a year making short DVD's (one commercial per disc or 30 seconds on 4.7)
I used a lot of CBR but now
trying several VBR schemes after reading these posts..

It is a science tho'
BECAUSE in some encoder when you raise the MEDIUM, the MAX is affected
In others, any setting is acceptable!

[poopyhead]

Because I spent over a year making short DVD's (one commercial per disc or 30 seconds on 4.7)
I used a lot of CBR

yikes...entire DVD-R with only 30 seconds of video??? isn't that kinda a waste...why not use (S)VCD instead.....since it's only 30 sec of video, you should be able to get a pretty high quality SVCD

[Cornucopia]

If you want the BEST quality on disc (not just pretty high), and you want the most compatibility with existing (incl. older) DVD players, SVCD would not be the way to go.

You only get ~2600kbps max vs. 9800kbps for DVD. That's 3.8x the bitrate for 1.5x the horizontal resolution.

You get all the cooler player features (Xtra audio trax, subtitles & video angles, player-dependent branching, auto 1st play, etc) with DVD.

You get a better and more popular 5.1 surround system with DVD.

Scott

[dcsos]

Poopyhead, these were for companies that didn't care about the waste on the disc and wouldn't even try an SVCD
One such job I remember was putting the Goldmember trailer (LIKE a minute thirty)on a DVD..then they ordered 20 copies.
And they wanted Authoring media ($15 a pop) what a colossal waste.
I'll bet 15 of theose DVD's we sent out were thrown out by now!

[poopyhead]

One such job I remember was putting the Goldmember trailer (LIKE a minute thirty)on a DVD..then they ordered 20 copies.
And they wanted Authoring media ($15 a pop) what a colossal waste.
I'll bet 15 of theose DVD's we sent out were thrown out by now!

the AMERICAN way