Video Bitrate Questions

[Tolwyn]

I forgot what the maximum bitrate for the stream in a standard DVD can be....

But... that's not exactly why I'm posting...

I understand that you have a finite amount of space on a DVD. 4.2GB, give or take.

And, your audio takes up so many kb/sec.
And, your video takes up so many kb/sec.

The duration of your video is directly dependent upon the bitrate settings that you choose at encode time.

No problem so far.

The higher the bitrate, the better the quality, the shorter the amount of time you can have.

So... if you have 2 hours of video, and you decide upon 192kbps of Joint Stereo (or Stereo) audio at 192kbps (standard?), then you're looking at around 4300 average bitrate.

This is, I would imagine, assuming a source at 720x468, 48Hz.
Obviously, the lower the resolution, the higher the bitrate you can use for the same amount of time... So, for my purposes, let's go with DV standards... It plays a role in my questions later...

Now to the questions.
Which produces the best quality? CBR or VBR? I would imagine that if I'm using CBR 8000, I'm going to get MUCH LESS total time on the DVD, but at a great quality; whereas if I use VBR, I can indicate my thresholds, accept satisfaction on an average, get good quality, and more time, right?

What is standard for commercial DVDs? And are we using VBR because most of us don't have dual-layer DVDs and we want more time on the thing?

And what is the bitrate for DV? I mean, is there a point of diminishing returns? If DV is ~5000 anyways, then I'm really not getting any benefit of using a bitrate higher than that, right? Now, I have to admit, I have no idea what the DV bitrate is.


If I'm using Hi8 as a source that is being capture as a DV AVI stream, what is the accepted bitrate thresholds to give me the best quality without having a lot of bitrate overhead? Obviously, my goal is to use JUST the RIGHT bitrate value to get the best results without over-allocating (and going beyond what most DVD players can decode/stream).

Right now, I'm sacrificing audio bitrate (128kbps) to squeeze in more bitrate for video. But if there are some "best practices" I'd really like to know what those are.

[Tolwyn]

Oh! I forgot part 2 of my questions.

If I'm creating a title (movie) made up of multiple clips, and all the clips are already encoded as MPEG2...

Do the clips in a single "movie" HAVE to be the same bitrate, or can I mix and match and still be okay?

Like... can chapter 2 and 3 be at a whopping 7000 with audio at 224kbps, but chapters 4 through 7 be at an average of 4500 with audio at 128kbps?

[Tolwyn]

By the way, I've since learned that resolution plays no role whatsoever in duration considerations.

Size = bitrate x duration
Makes sense to me!

[jimmalenko]

I forgot what the maximum bitrate for the stream in a standard DVD can be....

10.08 megabits (video and audio combined)

***

I understand that you have a finite amount of space on a DVD. 4.2GB, give or take.

4.377GB (4482MB) actually.

***

So... if you have 2 hours of video, and you decide upon 192kbps of Joint Stereo (or Stereo) audio at 192kbps (standard?), then you're looking at around 4300 average bitrate.

No. 4886kbits.



***

Which produces the best quality? CBR or VBR? I would imagine that if I'm using CBR 8000, I'm going to get MUCH LESS total time on the DVD, but at a great quality; whereas if I use VBR, I can indicate my thresholds, accept satisfaction on an average, get good quality, and more time, right?

Yes and no. First you need to make a decision - is quality absolutely paramount, and you'll use as many discs as it takes in order to retain the best possible quality, or would you prefer to sacrifice a little quality to aid in fitting everything to a specific number of discs (generally 1), or alternatively, are you prepared to cram the shit out of something in order to make it all fit to one disc ?

***

What is standard for commercial DVDs? And are we using VBR because most of us don't have dual-layer DVDs and we want more time on the thing?

That's generally why I use it. It's just more "efficient". Depending on your settings, it raises the bitrate to high values where it needs to, and lowers when it needs to, ending up with an average bitrate that you specify. IMO this is much better than using this same bitrate all the way through, because scenes that don't need much bitrate get the same as scenes that need plenty more and the result is a poor-quality encode. It all comes back to the bitrate you want/need to use as to which Rate-control method you use IMO.

And what is the bitrate for DV? I mean, is there a point of diminishing returns? If DV is ~5000 anyways, then I'm really not getting any benefit of using a bitrate higher than that, right? Now, I have to admit, I have no idea what the DV bitrate is.

I seem to recall someone quoting 25Mbps as DV's video bitrate (audio is 1536kbps PCM WAV).

***

If I'm using Hi8 as a source that is being capture as a DV AVI stream, what is the accepted bitrate thresholds to give me the best quality without having a lot of bitrate overhead? Obviously, my goal is to use JUST the RIGHT bitrate value to get the best results without over-allocating (and going beyond what most DVD players can decode/stream).

There is a chart at www.digitalfaq.com that shows graphs of bitrates, and it illustrates points where extra bitrate no longer has any effect. IIRC, Full D1 was at 8000kbps, but with a disclaimer that if there's motion, you might want to allow 1000kbps, so 9000kbps would be an agreeable value IMO.

***

Do the clips in a single "movie" HAVE to be the same bitrate, or can I mix and match and still be okay?

I'm not sure on bitrate, but I THINK they have to be the same frame size. If in doubt, just put each one in it's own track I guess.

[Tolwyn]

Awesome. Ok. Thanks.
And hey! I didn't use a bitrate calculator! That was all in my head!

Pretty close, I think.