Severe Artifacting after Compressor

[Bayne]

I have had an issue with this footage for the last couple years. After editing and outputting to compressor, I get severe artifacting every 15 frames. I think it has to do with the GOP, but I'm not sure what to adjust it to.

Now this only happens towards the middle of the m2v file. In the beginning of the file its not as prevalent. Also, Compressor is making my movie 720x404??? Would that also have something to do with the artifacting?

Machine: MacPro Quad 3.2Ghz Xenon with OSX 10.6.5
Original Footage: DVCPROHD 720p60 @ 29.97fps shot on HPX500
Transferred via: P2CMS
Log and Transfer: DVCPROHD 720p60 @ 29.97fps
Pixel Aspect: 920x720
Edited: FCP 6.0.6
Filters: Color Corrector 3-way
Export: Using Compressor
Compressor Settings: Apple Preset (No Changes) MPEG-2 6.2Mbps 2-pass + Dolby Digital Professional 2.0

That is the workflow for the file.

Here are some examples of pre and post footage. Not my most beautiful example, but this where I have most of my issues.

From FCP timeline
Frame 58245:

Still from m2v file
Frame 58245

From FCP timeline
Frame 58246

Still from m2v file
Frame 58246

From FCP timeline
Frame 58247

Still from m2v file
Frame 58247

So the image sequencing looks like this in IBBP:
Frame 1,2 - Blurry, Guessing?
Frame 3 - Sharp
Frame 4,5 - Blurry
Frame 6 - Sharp
...
Frame 13,14 - Blurry
Frame 15 - Horrible Artifacting.

Any thoughts?

 

[JeganRX]

I believe Demistate had a better idea of Compressor's rate control for MPEG-2. What you're witnessing is basically this: Compressor allocates bits within a GOP (and typically, 30fps MPEG-2 has a 15 frame GOP), but the quality degrades by the end of the group because Compressor has poor control over where to distribute bits. On top of this, your particular scene (water falls) is a notoriously difficult type of motion for a codec, so "bitrate pumping" as it's called (since the bitrate suddenly spikes, usually are every new keyframe), is easier to run into.

 

[Bayne]

Thanks for the response. With that said, why would it only happen further into the timeline and not straight out in the beginning. All of the footage is slow moving with little motion.

I have tried various IBP setups inside compressor and have found that Open GOP IBBP with a GOP size of 6 frames has less artifacting than the preset of a Closed IBBP.

Going to try that and see how it works. My biggest issue, is not that it is artifacting, but more towards the fact that it "builds" towards the middle of the timeline and doesn't start out with the artifacting straight away.

 

[Demistate]

Apple Compressor's MPEG-2 and H.264 codecs aren't the greatest. I can tell when someone compressed a trailer on a commercial blu-ray disc with Apple Compressor, since the final result looks so bad

Looking at your post you have two options:

1) hire a professional to compress your footage. (There are two in this thread, PM them for rates

2) Install bootcamp + Windows and try the Free HCenc encoder if you have the time. It is very good at using a dynamic GOP to help with problem areas like this. Also using a custom matrix can help with knowing which areas to focus the bits on to keep the detail there.

Interlaced 480P from a 720P at 60FPS is very hard to compress and look good on the disc.

Honestly, 6.2 megabits is very low for 29.97interlaced material. I would try 8mbps if you have room for it on the disc.

 

[Bayne]

Thanks for the info.

I'm going to try the Open 6 frame IBBP GOP and see how that works.

The project was 55mins and is now getting cut to a 22min pilot, so plenty of room on the disk. If that doesn't work, I'll get a hold of fellow board members.