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Compressor 3 & H.264 Strangeness

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Francis Sheehan
Compressor 3 & H.264 Strangeness
on Mar 15, 2012 at 6:37:55 pm

Mac Pro 2x2.93 Quad Core Intel Xeon 16GB RAM
Mac OSX 10.6.8
Compressor 3.5.3
Source codec: ProRes 4444 1920x1080 29.97
Destination codec: H.264 50000kbps
Type of destination use : Digital Deliverable (DGFastChannel)

I have 3 Mac Pro Systems with Identical hardware. I setup 3 Compressor Jobs on ONE System.
I send one job to each system (saved from compressor).

One System spits out 26mbps H.264 Files.
One System spits out 36mbps H.264 Files.
One System spits out 46mbps H.264 Files.

I cannot out for the life of me why compressor would be behaving this way.

Any thoughts?

Francis Sheehan
Palace Production Center


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Craig Seeman
Re: Compressor 3 & H.264 Strangeness
on Mar 15, 2012 at 7:32:59 pm

Without knowing the details, it's possible that the source can impact the final bit rate. The encoder may have some latitude to use more or less bits as needed. This is more so with VBR (Variable Bit Rate) encoding. I know some encoders can be "forced" to pad bits to hit a target rate (not something Compressor has as a feature though). You can use the same setting on a file with fast action sports with heavy motion graphics and on a file with a talking head end get different bit rates in the resultant encode.

Again, I can't say for sure that's what happened here but generally I don't find it unusual to get different bit rates using the same setting on different source files.



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Francis Sheehan
Re: Compressor 3 & H.264 Strangeness
on Mar 15, 2012 at 8:01:33 pm

Thanks for the input. This project is making me a little paranoid given the fun i have had with it over the last 2 days.

Francis



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Craig Seeman
Re: Compressor 3 & H.264 Strangeness
on Mar 15, 2012 at 8:40:25 pm

I can understand especially when there's file based DG delivery.

BTW and the most recent spec sheet I have from DG (which is admittedly a year old) their H.264 specs are 422 chroma, not 420. Has that changed? I ask because Compressor doesn't do H.264 422, only 420. Of course it's possible they may overlook that.

I recently had a Comcast directly delivery and their H.264 spec is also 422. I delivered 422 (using Episode) and it failed. I then delivered 420 and that passed.

I also deliver to DG although I had been using MPEG2 Program or Transport Streams. I'm wondering if DG's H.264 422 is like Comcast's (as in they'll accept 420 even if that's not the spec they promulgate).



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Francis Sheehan
Re: Compressor 3 & H.264 Strangeness
on Mar 15, 2012 at 9:08:00 pm

I have yet to have a reject of compressor H264's for HD. I have been delivering them to DG for over a year. For SD i have been doing MGEG Program Stream out of Media Encoder for those deliverables.

Like everyone else's specification sheets, they are littered with contradictions. It can be hard to tell what really matters to them.

Francis Sheehan
Palace Production Center



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Craig Seeman
Re: Compressor 3 & H.264 Strangeness
on Mar 15, 2012 at 9:33:12 pm

[Francis Sheehan] "Like everyone else's specification sheets, they are littered with contradictions. It can be hard to tell what really matters to them."

Is this every the truth!
I've been using DG for about 4 years. It's good to know I can "break the rules" and deliver H.264 420 to DG as I found Comcast accepted as well (despite the spec sheet).



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