Which results in better quality encoding:constant or variable and why?

[Canon GL-2 Guy]

I'm relatively new to the world of encoding and need to ask before getting mired too deep into this.

If I have a dv-avi file (which will be eventually broadcast on cable) that is less than an hour (or just under),to date usually,(because I don't know yet what's best or ideal)I use a variable bitrate between 8,000-8,200 kbps. In my opinion only,the results are good or somewhat beyond that but not great.Maybe I'm expecting too much?My goal is quality.

What is the max bitrate setting should be used?At some point/threshold does it make much of an appreciable difference?Can less be more so to speak?What settings should I use?

Some of these programs limit how high one can go.

Is 2 pass encoding preferrable or does it chew up more processing time for minimal gain?

Is constant or variable better and what are the pros and cons of each if any?What's best from your experience?

Sorry,just trying to get out of the fog/woods here and make some progress.

I want to exercise the right options and use the right programs.

All opinions,suggestions,reccomendations and responses welcome.

Thank you.

[ZippyP.]

Here's the theory/logic of variable bitrate (VBR) vs. constant (CBR).

Each scene in a video needs a different minimum bitrate in order to maintain optimum quality. High motion scenes (and jumpy camcorder footage) require a high bitrate to look good while still shots need a lot less. VBR will apply more or less bitrate as required by each scene so that no bits are "wasted", this helps if you want to squeeze as much video as possible on a single disk. CBR will apply the same rate throughout, if it isn't high enough then some scenes will suffer. If a scene has too many bits then it is simply wasted, but it does not affect the video. If you are not concerned about space then by all means use CBR and set the rate nice and high. If space is a concern and you cannot set the CBR bitrate as high as you'd like then it might be better to use VBR. Personnally I use 2-pass VBR when required as the file size is predictable. CQ-VBR is faster (1-pass) but the resulting file size is unknown.

There is always a point where increasing the bitrate yields little quality gain until there is no improvement at all. Where that point is depends on the encoding program, the codec (mpeg, divx, dv etc.), the source (TV, DVD, camcorder...) and how fussy you are with regards to quality. It's basically trial and error and everyone has a different opinion because we all perceive quality differently.

Hope that helps.

[Cornucopia]

The rule of thumb is (there are exceptions and variations):

All other things being equal,

VBR and CBR are basically the same FILESIZE-wise for the same AVERAGE bitrate. (But not the same quality-wise)

and

VBR and CBR are basically the same QUALITY-wise, when the VBR PEAK(MAX) bitrate = CBR bitrate. (But the filesize will likely be much smaller for the VBR).

Try out small sections and see for yourself.

Scott

[daamon]

If I have a dv-avi file (which will be eventually broadcast on cable) that is less than an hour (or just under),to date usually,(because I don't know yet what's best or ideal)I use a variable bitrate between 8,000-8,200 kbps. In my opinion only,the results are good or somewhat beyond that but not great.Maybe I'm expecting too much?.

Done properly, you can get high quality MPEG2 that looks virtually identical to the source DV AVI. The words "done properly" also include all of the preparation prior to shooting and the shot itself as well as the encoder and its settings.

Typically, CBR up to (note: not necessarily "at") the max is used for footage of an hour or less. If the footage is longer, CBR can still be used but you'll need a lower bitrate, lowering the actual (and possibly visible) quality.

Anything below around 4,500kbps and you may start getting quality issues. Only you can decide what is acceptable, and therefore what your lowest approximate bitrate will be. Different footage require has bitrate needs, so do not fix the lowest you'll work with.

This link can help as a guide for when to use CBR vs VBR:

http://dvd-hq.info/Calculator.html

What is the max bitrate setting should be used?At some point/threshold does it make much of an appreciable difference?Can less be more so to speak?What settings should I use?

Look under the "What Is... DVD" link at the top left of the page - the max allowable is described in the DVD spec. The max you use depends on the running time of the footage and how big you want the end filesize to be. This can be calculated in the VideoHelp Bitrate Calculator.

Is 2 pass encoding preferrable or does it chew up more processing time for minimal gain?

I tend to use 2-Pass VBR for footage that's over around 90 minutes for a single layer DVD. This aims for an average bitrate (that you set) and so the quality is as good as it can be (within the max, min and average) you set - as a result of being longer than about an hour.

Is constant or variable better and what are the pros and cons of each if any?What's best from your experience?

Neither are better - VBR aims for an average bitrate. A CBR encode at that same bitrate will produce the same quality.

[edDV]

Describe your source and the clip length in minutes that you MUST fit to a MPeg2 DVD. We can then offer advice on method and bitrate.

Critical info.

Camcorder model number?
Handheld or tripod?
Any zooms or pans?
Dark lighting?