Maximum / Average bit rate difference

Hi Cario,
good to see you around again.

Is there any rule about the Maximum / Average difference ? Is 3 Mbps a good choice?

There are guidances and suggestions, however, it depends on the type of project you are on and the length (10 minutes or 160 minutes? that makes a difference) .

You did not mention how long your project is, however, there is a tool that can help you deciding a proportionate max. ad av. bit rate, it is called Bit Budget.

http://home.comcast.net/~c.linke/bitbudget/

Also there are some old and new articles that might help you understand more,

http://www.dvpa.com/public/315.cfm
http://www.kenstone.net/fcphomepage/compressorwarmouth.html

Hope that helps,

G.

For projects up to an hour you will get the best quality using a Constant Bit Rate (CBR) of around 7.5 to 8 Mbps.

Every bit of encoding will be done at top quality and it will be done in half the time.

VBR is only for people who have to make the most of limited space when producing DVDs considerably longer than an hour.

VBR doesn't produce high quality, it merely minimises the quality loss when you make long DVDs.

Here is a simple explanation that might help. If you have an average of 5 and a max of 8, then for every part that has to be encoded at 8 another part must be encoded at a level BELOW 5 to counter the 8mbs section. If you have too great a spread in your average to max bit rates, you run the risk of having portions of your movie encoded at a very low bit rate. This is not good. If you keep the ratio fairly close you can ensure that you will not go too far below your target (average) bit rate. I would not have the average be half the max. You are setting yourself up for some very low sections. Take Apple's suggestion, of having a 1mbs difference. If you have, say, 5 and 6. If half your movie is fast motion and gets encoded at 6mb/s, and the other half is not too fast, it will all be encoded at 4mb/s. Add all the elements together and divide by 2 and you get 5, which is your average. 4mb/s isn't too bad for scenes without a lot of motion. But if you chose 4 as average, and then doubled that for the max, at 8. Then the fast half would be encoded at 8mb/s and the remaining would be encoded at 1Mb/s, to average out at 4. I would not want the 1mb/s sections anywhere near my 8mb/s sections.
Of course these are ludicrous examples, but they illustrate the point properly.

Message was edited by: RedTruck

It would be ideal for fast movement because you are using the maximum bitrate all the time so the fast movement will get exactly the same treatment as with VBR.

It's just that slow movement will also get maximum bitrate which does no harm but might be considered a bit of a waste.

However, as long as the DVD is not much more than an hour it doesn't matter as the DVD will have space.

VBR is purely for DVDs over an hour long.

Think of a 2 hour DVD. With CBR you would have to use 4 Mbps which would give rather poor quality especially with fast moving scenes.

VBR is a means of giving those fast moving scenes a bit more quality (in the form of a higher bitrate than 4) whilst the slow moving scenes get a lower bitrate which does not matter too much.

Of course it has a CBR setting. It's there for all mpeg2 options. You set it in the quality tab like you said. If you don't want to create a custom setting, you can use the presets as a template and then change whatever options you want, as you stated. You answered your own question.

cariocastyle wrote:
I`m planning to use a 2-pass VBR Best, 4.5 average and 7.5 maximum, for a NTSC SD DV project that `s going to be replicated. Will it be better for example if I use : 5.5 average and 7.5 max?

If you're going to produce replicated discs, you'll have the luxury of cranking up the bit rate to 5.5 average / 8.5 max. (The 7.5 max is a limitation for DVD-Rs, because they less reliable if you push the bit rate over that 7.5 mark.)

That said, I standby the 3 Mbps difference as a rule-of-thumb (especially if space isn't an issue). Of course, salt to taste depending on your content.

If you wish to use a CBR setting: Inspector window>Encoder> quality tab > Mode>popup menu>top of the menu>One pass CBR.

Hi there,
good to have you back 😉

Thanks G.

Just noticed you're one of the Top 10 responders on the FCP forum. Nice work!

You are a great example of top user for me and I truly mean it.
Thanks for YOUR nice work,

Luca