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H.264 How do I Control/increase Bitrate?

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Dixon Johnston
H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 7:01:55 pm

Hi everyone, Ive searched the posts but cant seem to find what Im looking for. Most posts are trying to DECREASE bitrate, whereas Im trying to increase it to meet media outlet requirements of minimum bitrate 8Mbs.
I have been uploading a lot of commercials via ftp lately. What I've found is that the bitrate varies tremendously although I am using the same settings.
For example,
I compressed a 30 sec spot this morning, using FCP-QT Conversion, h.264, quality set to 'best' and multi pass. It came out at about 10MBS-PERFECT!

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.
Ive also tried using compressor, but get the same type of results. I am mainly wondering how I can more accurately control the output bit rate either through QT, FCP or Compressor.

Im working with an uncompressed (8 bit) source file 1.06G which shows 169Mbs.

If compressor is the solution, how do I control it when it only offers "best" and "multipass" as options-which seems weird because you can be more precise in the h.264 DVD Studio preset. That does not give me an interlaced option.

Any help is appreciated!

Dixon




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)


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Craig Seeman
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 7:40:49 pm

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





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Dixon Johnston
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 8:47:02 pm

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)


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Daniel Low
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 8:12:45 pm

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


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Dixon Johnston
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 8:57:36 pm

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)


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Craig Seeman
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 9:09:13 pm

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.





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Dixon Johnston
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 10:12:56 pm

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)


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Craig Seeman
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 10:30:30 pm

Looks like you're setting it to 200,000kbps. Set it to 20,000
In Compressor make sure you set frame size to 720x486 NTSC CCIR 601/D or in Quicktime NTSC 720x486 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 720x486 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.



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Craig Seeman
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 10:38:18 pm

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.



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Daniel Low
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 10:36:04 pm

[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)



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


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Craig Seeman
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 10:42:08 pm

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 1920x1080 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.


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Daniel Low
Re: H.264 How do I Control/increase Bitrate?
on Jul 15, 2009 at 10:59:10 pm

Oh, I didn't doubt that they were probably re-coding it, I was just pointing out that high quality was possible at considerably lower rates than were being discussed.

Mezzanine for me is 50Mb/s MPEG-2 but I'll sometimes go to 30Mb/s.

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


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Dixon Johnston
Re: H.264 How do I Control/increase Bitrate?
on Jul 16, 2009 at 6:57:22 pm

Thanks guys, for all your help. Thought Id let you know where I am with this.
I tried yet again, using the specs provided, and got no improved results. Not sure I really understand how to "trick it into upping the level". The best end result was exporting via FCP QT conversion with compressor quality set to "best", encoding set to multi-pass and "Automatic" Data Rate yielding a 6550kbs file. So thats what Ive uploaded, and we'll see if anyone complains.

Here is another mystery Ive come up with. This particular 30 sec spot also had a cutdown 10 second version-where literally, the last 10 seconds was the product-no edits or alterations. I exported using FCP and the same EXACT settings described above. It yielded a 7238Kbs product-higher than the 30.

Not willing to let it go, I tried again through Compressor and it kills me that I can adjust a bitrate slider in the H264 Studio Pro presets but cannot do it in any of the interlaced SD 29.97 720x486 settings. (or at least I havent discovered a way to do it). I did try the Studio Pro preset, and as expected, got a 59.94 frame rate file at 720x480, average bit rate slider set to minimum 12Mbps. The result was 11.84 Mbps file, but was the wrong frame rate and aspect for my purposes-AND it took 3 HOURS to Transcode. Pressing on-I exported that file, to correct the frame rate and aspect, which got me a 5560Kbps file (I suppose because its half the fps). This is about the same as MOST of my earlier attempts.

Im giving up for now after 15 attempts, and will use it as ammo (whether justifiable or not) to get an Intel Mac. Is it possible all the varied results is actually CPU related?

I really appreciate all of your advice, and Im sure I'll be looking to the cow as we transition to a P2 world. I will check back on this post to see if you guys have any more theories or solutions.

Thanks again.
Dixon

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)


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