H.264 How do I Control/increase Bitrate?

[Craig Seeman]

In Quicktime Video Settings change Data Rate from Automatic to Restrict to and then type in the bit rate you want.

[Daniel Low]

[Dixon Johnston] “This afternoon, another 30 sec spot with the same settings will not exceed 6.5Mbs. Ive tried ‘restrict to 15000kbs” as an experiment, but it is not helping my bitrate problem. “

Do you use CBR or VBR rate control?

Simply put, your content didn’t require anymore than 6.5Mb/s. The only way to ensure a datarate is to use an I-Frame only format, otherwise known as ‘constrained’

Examples are:
DV
DVCPRO
IMX

These are based on MPEG-2

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[Dixon Johnston]

Thanks for the quick reply, but (previous post) “Ive tried ‘restrict to 15000kbs” as an experiment, but it is not helping my bitrate problem. ”

I just did it again to make sure, and set restrict WAY up to 200000kbs and its still exporting at 6500kbs.
Is there any other info I can provide to help track down the problem? Does keyframe rate matter?

Dixon Johnston
Creative services Director-WRIC

Dual 2.0 G5, 4G RAM
OSX 10.4.1, FCP 5.1, QT 7
AJA Io-Beta SX (SDI)

[Dixon Johnston]

My most recent attempts have been exporting through final cut’s Quicktime Conversion feature, where I dont see VBR vs CBR as an option. I would assume its CBR. I am not setting “prepare for internet streaming”. Does that help?

Dixon Johnston
Creative services Director-WRIC

Dual 2.0 G5, 4G RAM
OSX 10.4.1, FCP 5.1, QT 7
AJA Io-Beta SX (SDI)

[Craig Seeman]

I’ve delivered to HD Spots to DGFastchannel Chicago at 50,000kbps using Compressor.
This is really all there is to it. Quicktime has very limited controls. I checked my file in Media Info and it was 50000kbps Main@L5.0. Quicktime sets Profile and Lever automatically. No user control

BTW Frame Reorder is B frames basically. You can turn that off but you can’t do all I frame. DG wants the B frames.

I can’t help but think there’s something you’re not telling us.

[Dixon Johnston]

Daniel, So you’re saying that the file has been basically maxed out for the codec and it doesnt require any higher bitrate to maintain its quality? Which makes sense in a way because the video is graphic based-fairly simple text effects over some composited stills, whereas the 1st one I compressed this am that had a much higher bitrate-was all live action video.

If this is the case, do you think that the minimum 8Mbs requirements by the media outlets would actually be a problem or contested? As I understand it, if the bitrate is too low, when it runs off the servers for broadcast, the image can smear, blur, or jitter.

Craig, I hope to give you all the info I can to figure this out. Let me know what else I can provide to solve the problem. When you send though Fast Channel, how do you control the parameters in Compressor? I only know of this route (see bottom screen shot).
As you’ll see below, I got a slightly lower bitrate (5500kbs) than before (6500kbs).
I did the process again, so I could create these screen shots.

Export via FCP

Export via Compressor, inset is the QT Info, youll see that compressor estimated the bitrate at the 20000 MBS, but the QT result was 3640Mbs

Dixon Johnston
Creative services Director-WRIC

Dual 2.0 G5, 4G RAM
OSX 10.4.1, FCP 5.1, QT 7
AJA Io-Beta SX (SDI)

[Craig Seeman]

Looks like you’re setting it to 200,000kbps. Set it to 20,000
In Compressor make sure you set frame size to 720×486 NTSC CCIR 601/D or in Quicktime NTSC 720×486 4:3
Set Audio to Linear PCM.
Note the KeyFrame rate setting of 24 in the settings I posted (as odd as that would seem).

Since Apple automatically sets Profile/Level I’m thinking something about your setting is limiting that.
If this is for Broadcast you want to keep the nonsquare 720×486 frame size and aspect ratio.

DG Chicago only accepts H.264 for HD (DG National is only SD and requires MPEG-2 Program Stream). DG Chicago requires 50,000kbps though and that’s exactly what I got despite the fact that in other compression apps the slate and black would have brought down the bit rate.

[Daniel Low]

[Dixon Johnston] “Daniel, So you’re saying that the file has been basically maxed out for the codec and it doesnt require any higher bitrate to maintain its quality?”

Correct.

I’d also like to point out that H.264 is a highly efficient format and the datarates you are delivering are HUGE for the given content and frame size.

Like I said in previous post, I’ve seen stunning 1080p at less that half that datarate. (But you need to know exactly what you are doing to achieve that).

That said, what the customer wants, the customer gets. (Unless they are totally wrong or way off the mark)

__________________________________________________________________
Two years from now, spam will be solved. – Bill Gates, World Economic Forum 2004

[Craig Seeman]

I tried my own suggestions with one of my files.
The resultant bit rate is 15,830kbps. A little low for 20,000kbps but that’s closer than what you’d been getting. Give the settings a try.

[Craig Seeman]

Daniel it may be they’re doing a re-encode.
I thought DG H.264 settings at 50,000kbps was a bit over the top even for 1920×1080 but they’re taking that file and re-encoding to MPEG-2 Transport Stream. I don’t doubt they want the file as “mezzanine” and they may know what kind of quality hit their encoder is going to do to it. Basically they’re taking advantage of H.264 efficiency to avoid needing huge 8-Bit Uncompressed files FTP’d to them.

And yes Compressor may be “maxing” out given his settings. That’s why Compressor is a very limited tool. You need to “trick” it into upping the Level.