Determining Proper Settings in Compressor

[ This article was first published in the 2004 issue of
Larry’s Monthly Final Cut Studio Newsletter. Click here to subscribe.
Substantially updated January 2006, with information on problems
with Compressor 2. The update is the second half of this article. ]

I first planned to cover Compressor in two parts (last month and this month). However, the more I got into it, the more I realized there was more to talk about, so we’ll continue this series for another month, at least.

This month, I want to give you some suggestions on proper selection of compression bit-rates; as well as how to improve the compatibility of the CDs and DVDs that you burn.

Bit-rates

While the DVD spec allows us to set bit-rates as low as 2.0 Mbps and as high as 9.0 Mbps, there are some general rules you can follow to improve the quality of your videos, while still keeping file size small.

Here’s the challenge: older DVD set-top boxes and computers who are playing DVDs using software decoders have problems with fast bit-rates. In fact, it’s possible for you to compress a video with such a high bit rate that it can’t be played back.

So, to make sure that your DVDs will burn properly:

1) Set your average bit rate between 4.0 Mbps and 6.5 Mbps. (The lower the number, the more video you can squeeze onto your DVD. 4.0 Mbps should allow a little more than 2 hours of video.)

2) Make sure your peak bit-rate doesn’t exceed 7.5 Mbps. 7.0 Mbps is better. (I use 7.2.) This makes sure you have enough head-room to compress active scenes without creating so much data that computers or older DVD players can’t keep up.

You change your bit rate settings in Compressor by:

1) Open Compressor

 

 

2) Click on Presets

 

3) Twirl down the Preset you want to change (a preset contains compression settings for audio and video separately)

 

 

4) Click the Encode tab

 

 

5) Click the Quality tab

 

 

6) Change the bit rate settings to match your preferences. Remember, 2-pass VBR gives better quality and smaller files, but takes longer to compress. I always use 2-pass because I am always interested in the best quality. This screen shows the settings I use for longer videos.

When you have a shorter movie, you can increase the lower bit rate 6.5 or even 6.8. However, DON’T change the peak rate.

Burn speeds

Again, to maintain maximum compatibility with other players, follow the following rules:

1) Don’t burn too fast. Burning at slower speeds increases accuracy and compatibility

2) Match the speed of your media with the burning speed of your drive (especially for DVDs)

While DVD Studio Pro, iDVD and the Macintosh operating system don’t allow you to set the burn speed of your internal disk burner, programs like Roxio Toast do. However, even the Mac programs don’t burn at the fastest speed your drive may support.

For CDs, your best burn speed is 16X. For DVDs, the best burn speed is 1x or 2x. What does “best” mean? It means that when you burn at these recommended speeds, you will have fewer errors and drives other than your own will more likely be able to play back the disks you burn.

Remember, your goal is not to get done more quickly, it’s to make sure that whatever you burn to disc can be played on other systems — or on your system, months and years down the road.

By the way, to answer Jim Perry’s question, DVD Studio Pro uses the same compression engine as Compressor. The benefit to using DVD SP is that, IF you have a fast enough computer, it will run in the background. The benefit to using Compressor is that you have more controls and can easily create batch files to compress the same video into multiple formats.

Update: Compressor Settings and Issues

Steve Browne, from Australia, wrote in with a question on Compressor which sparked this next technique:

I read your website and also have done all your tutorials on Lynda.com, as well, of course, buying one of your books! So I appreciate all the advice you have given. I also appreciate that your voice is easy to listen to!

 

Anyway in your next newsletter can you write something on Compressor 2? There is a lot of talk on the Apple discussion site that 2 pass VBR gives artifacts, especially on transitions and is generally to be avoided.

 

What would your recommendation be? For a commercial production what would you use, or would you go to BitVice?

Karl Arndt also chimed into this discussion:

At our Final Cut Users Group meeting the question of 2-pass encoding came up when doing small (short) projects. Our guru master, Jerry Hofman as well as others, felt with short programs, anything under 60 minutes, that there was no advantage to using 2 pass VBR. Single pass encodes did not affect the quality of the encode at all and the speed of the encode was much faster.

 

I know from your Final Cut tutorial video, which I live by, that you go into great length on setting up the parameters of High Quality encoding. Do you agree with Jerry regarding the short program assessment? What bit rates would you adjust to the single pass encode?

Larry replies: I was all set to answer this question, when I got a great email from Uli Plank which helps explain the problem.

[Larry wrote:] My recommendation is to set the average data rate to 5.5 and the max data rate to 7.2 — regardless of whether you are burning or replicating(i.e. going to a glass master). There’s no advantage to going much higher and there are significant problems with data rates that are too high.

Uli responds:

If I may chime in on this, with my years of experience in DVD-authoring as well as teaching it (and being the leading author on DVD-production in German language).

 

I’d like to add a few things, regarding Compressor 2 in particular. In their effort to tackle the problem of overshooting data-rates in C1, Apple seems to have ruined the quality of 2-pass VBR encoding to some degree. I’ve seen quite a few cases now where 2-pass VBR doesn’t look as good as the simple 1-pass (which is not strictly CBR, but close). So, my first recommendation is:

 

If you have the space, use 1-pass over 2-pass VBR until Apple fixes the problem. You are absolutely right about staying below 8 mbps (including all soundtracks!) if one is going to duplicate (i.e. burn) the DVD’s. And definitely avoid PCM audio, always use AC-3 for DVD-/+R. If you want to play even safer, stay under 7.5 mbps in the sum. Going lower won’t help with compatibility on critical players, rather try different brands of DVD-/+R.

 

If you are going to replicate (i.e. press the DVD’s from a glass master), you are allowed to go higher. The sum of all streams should not exceed 10.8 mbps in this case, every spec-compliant player is supposed to play such DVD’s. But don’t expect too much of an improvement in quality if, let’s say, [you are] using 9 mbps instead of 7.5 for your video. The visible improvement will be far lower than the change from 4 to 5.5, for example.

 

You’ll rather want to use the higher data-rate for additional soundtracks in higher quality formats, like PCM or DTS (if the client is ready to pay for it, the encoders are costly).

 

If you are still unsatisfied with your video quality from Compressor, try another encoder. On the Mac, there are BitVice (www.innobits.se) and MCC (www.mainconcept.com), both of them have watermarked demo-versions online.

 

The best software encoder is, unfortunately, still only available for the PC (Cinemacraft). But if you have very discerning clients and regular encoding jobs, it may be worth the investment to set up a fast PC (even with the basic version of that encoder) and use it for encoding only while doing your creative work on the Mac.

 

Finally, please remember the good old rule of GIGO (garbage in -> garbage out): if you feed it bad video, no change of data-rate and none of these encoders will really help. The worst thing is any kind of video noise, it’s pure poison to MPEG. Any levels of [camera] gain higher than 6 dB on most camcorders is asking for trouble.

Larry, again: Also, in the Late-Breaking News PDF on Compressor that is available on Apple’s website, there’s this warning from Apple:

Using all Best settings may result in unexpectedly long processing times. If you are reducing the frame size in addition to deinterlacing the frame, Fast or Better will likely provide sufficiently high quality, depending on the amount of downward resizing.

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