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artifacting during Mpeg2 compression with Compressor

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Shilpi Roy
artifacting during Mpeg2 compression with Compressor
on Dec 9, 2008 at 9:18:41 pm

Hello everyone,

I have a 15 min short film (master is HDCAM) that I am encoding through Compressor to Mpeg2. I've been playing around with bit rates to see what the best image I can get is, and playing it on several TVs. What I've noticed is that artifacting seems to happen differently on different TV's. I'm not so concerned with fades and dissolves, but most often there will be a flickering line around the edge of an object which really annoys me.

Seeing as this happens to different degrees on different TVs, I'm not really sure what I can do to try and combat it during encoding, except set my bit rates as high as I can without choking my DVD player and hope for the best.

I'm also wondering if this is a problem that will be nonexistent if I just get the movie encoded professionally on a hardware encoder? The replication company I'm currently looking at uses StreamZ. I've been reading all the posts about hardware vs software encoding here, but I'm still unsure what the best process is for me. Any thoughts on either subject would be great. Thanks!



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Daniel Low
Re: artifacting during Mpeg2 compression with Compressor
on Dec 10, 2008 at 12:14:06 am

StreamZ will only better Compressor if you feed it a signal from a deck rather than a file. Compressor has the tools to do a much better job with file based stuff.

Please give more details on your source, your settings and the problem.

__________________________________________________________________
Please post back saying what solved your problem. It could help others, and saying 'thanks' is free!


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Shilpi Roy
Re: artifacting during Mpeg2 compression with Compressor
on Dec 10, 2008 at 12:44:12 am

I onlined to HDCAM (it was also shot on HDCAM), and had my online editor give me a full res quicktime out of the Avid, using the DNxHD codec. I then converted that to Apple Prores HQ (using Compressor) so that I could work easily within FCS2. It is the Prores QT (around 16GB)that I was compressing down to MPEG2.

In terms of my settings for the MPEG2 settings for Compressor I chose a Two-pass VBR Best with an Average BR of 6.8 and a Max of 8.0 (which is definitely pushing it, I know). My motion estimation is Best. GOP at 15 (Closed structure).

One thing I'm not sure about is "field dominance." It was on Progressive. Automatic was grayed out and I wasn't sure if I should do "top first" or "bottom first."

The problem I'm having is that on certain TV's different images will retain a flicker around the edge of objects for short periods of time. It usually won't encompass the entire object or person, just part of them. On low end TV's these flickering edges are worse then on Hi end TV's. Sometimes it's so small you can only see it if you're sitting closing to the TV, but other times it's noticeable if you're at a normal distance. When played on computers I think the flicker is virtually nonexistent. It looks a little bit like the flicker you see when small credits are being scrolled vertically, (but that flicker is around the edge of an object) if that helps any.

Do you guys think this is the best I can do in terms of compressor settings?

In terms of a Hardware encode, it would be straight from a deck, off my HDCAM master, and I believe they can do 2 pass VBR.

thanks!







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Daniel Low
Re: artifacting during Mpeg2 compression with Compressor
on Dec 10, 2008 at 7:50:13 am

Was it shot interlaced or progressive?

The artefacting you are seeing doesn't sound like interlacing it could just be the result of poor down-scaling - any chance of posting a screen grab?

__________________________________________________________________
Please post back saying what solved your problem. It could help others, and saying 'thanks' is free!


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