Pulsating artifacts in MPEG-2 Output

(I'm running 3.5.3, on an 'early 2009' 2.66 Mac Pro 8-core, FCP 7, 8 GB Ram)

Hello,

I'm having a strange problem with Compressor in outputting MPEG-2 files for DVD creation, something I've done now for years without issue. I'm creating the MPEG-2 from a 1920x1080 ProRes QT output of my 60-minute film, rather than 'sending' directly from FCP to Compressor because of another problem (titles generated in FCP aren't the correct aspect ratio in the final MPEG-2, whereas the video footage is correct).

Anyway, I'm seeing artifact-riddled frames happening at regular intervals in certain parts of the film, quite randomly; occurs in both motion and stationary shots. One frame will suddenly just go blocky and glitchy, with the frames surrounding it looking fine. This will repeat for a while, creating a 'pulsing' effect, and then disappear for a while. I'm reading that a few other people are having the same problem on the Apple discussion boards, but no clear cut answers. One person suggested selecting "Progressive" in the Field Dominance setting in the Inspector, rather than "Automatic", which I plan to try out.

I do notice that the frames that go berserk are exactly in proportion to my GOP; in this case, 7, so that every seventh frame is the bad one. Again, I've made MPEG-2s about a million times and never encountered this, but I haven't done so on this machine too often. It doesn't make sense to me that this would happen, so I wonder if it is has something to do with Snow Leopard disagreeing with Compressor or something mysterious and magical like that.

Any ideas? Thanks for your time. Bonus points for anyone that can clear up the aspect ratio problem with the title generated-text mentioned above...

Greg

Did anyone ever get a solution to this? I've started having the same problem, locked off extended single cam shots start pulse artifacting at randompart way through - I thought the FCP suite was a "professional" bit of kit, I don't get this with Avid or Premier on a Mac - WTF? any help appreciated.
Steve
www.whistlingmule.com

a quick web search shows similar problems going back to late 2008, I must have produced over 100 master DVD's since then and this is the first I've seen, I hope to god I just didn't QA the rest well enough. About 75% through a 3.7 GB 1080p QT XDCAM EX clip - all locked off talking heads or slow pans > 6 seconds per frame view I get pulsing block artifacts like a heartbeat. Unacceptable for delivery with deadline tomorrow - WTF??? Maybe a bug in the VBR algorithm that just appears after extended still shots? I might try a CBR encode or else???
HELPPPPP
Steve The Mule
www.whistlingmule.com

A wild guess here. If you're using a qt reference movie, you can try using a self contained qt movie instead. And make sure you send "dvdsp markers" when you export from FCP.



www.strypesinpost.com

Hi Strypes, thanks for the suggestion, I'm sitting on a job in southern Spain with a MacBook Pro 4 GB unibody intel dual core 2.46 Ghz machine hooked up to some esata RAID arrays, latest version everything OS and FCP 2 and an early morning deadline. I'm dealing with 85 mins of edited XDCAM EX material and was just going through the motions a few hours ago to get a DVD copy ready for tomorrow morning when I noticed the pulsing. I've since scoured the web and found a) its not uncommon b) I haven't found a solution only suggestions. Originally I just sat back and let FCP send to compressor at the best for 90 mins 2 pass VBR preset, this generated the pulsing artifacts. This time I exported a QT reference movie at the current timeline settings and am almost finished a 6.2 Mbs CBR Compressor encode.
Its been hinted the problem is with VBR and motion estimation during particular shots after a certain time duration but...... We'll see what the CBR looks like. If this fails or looks crap then I'm working on my later night (its 23:23 here) plan c and d. Plan c involves transcoding in compressor first to Pro res then using 'job to target' try a 2 pass VBR encode or else buy and download Innobits Bitvice Mpeg 2 compressor. Do you have any experience with that? At this point in time all suggestions appreciated
Cheers
Steve

Oh and Greg, sorry I forget to write this above but I've had font problems like that before and cured it by deleting all the font caches at either the system or FCP level and all render files.

Update at 01:38
A CBR encode in compressor at 6.2 Mbps works well with my material. It also reduces encode time dramatically so I'm testing a 7.2 Mbps CBR encode now, 85 mins source take around 100 mins to encode so if I can calculate the bit budget correctly I think in this case not only am I out of the fire but some scenes are looking better using CBR - not a lot of fast action anywhere but lets wait and see. I'd love to know what causes that VBR artefact pulse - a bug? fixable? Shouldn't Apple get their act together over this?

So the solution in summary - use the Compressor 6.2 Mbbs preset as a starting point but change from 2 pass VBR to one pass CBR at the best bit rate you can.
This is the first time in 100's of DVD's using 2 pass VBR that I've noticed this artefacting problem.
Maybe try Cinema Craft MP encoder plugin or BitVice

Cheers
Steve

Did you export with DVD sp markers? That will let Compressor know where the scene breaks are.



www.strypesinpost.com

normally no problem with chapter markers - do that in FCP, send to compressor, since FCP 2 its been find but exporting a stand along or reference QT file has revealed another bug. If I export from FCP with 'all markers' and then import to compressor all chapter markers are lost. If I export with only 'chapter markers' then its fine. I haven't tried exporting only with 'dvd sp markers' What would that give me?

PS 85 mins with the particular template and audio menu assets I'm using is fine on a DVD 5 at 6.2 Mbps CBR leaving 400 MB free but at 7.2 Mmbps I miscalculated at 3 in the morning and its 100 MB too big - AARRGGGGGGGHHH - so I'm doing another encode at 6.8 Mbps to compare with 6.2 - I can ride with 6.2 if needed, it still looks good.

>I haven't tried exporting only with 'dvd sp markers' What would that give me?

All markers. Yea, I know, don't ask. The most important thing that compressor needs is cut/edit point markers, as Compressor doesn't do scene cut detection, which is essential to long GOP encoding. Exporting with DVD sp markers will retain the metadata of the location of each cut point (edit/cut markers), allowing compressor to more accurately create a new GOP at each edit point. Not sure if this is related to your issue.



www.strypesinpost.com

Thanks Strypes,
good to know, I posted off this morning a 6.8 Mbps CBR encoded DVD which was fine, to be honest there wasn't much difference with this particular content between 6.2 Mbps and 7.2 Mbps CBR. The encode was made from a QT reference file exported from FCP 2 with chapter markers only, this seemed fine but I will look into using DVD sp markers.
Regarding the pulsating artefacts, the fault seems to lie in compressors 2 pass VBR process so if anyone has any more insight or actual solutions rather than work arounds I'd love to hear. I'm now dreading the next project encode in the UK, if I do 2 pass VBR and wait X hours and then QA and find more pulsating artefacts I'll freak out. I've sort of lost confidence in compressor. I'd like to have that confidence return or maybe bite the bullet and go Bit Vice or Cinema Craft mp?? opinions?

Cheers
Steve

Hi everyone,

Sorry I haven't responded myself, I hadn't received a reply to my question in some days so forgot about it.

I read somewhere that you need to select "Progressive" in the field dominance selection in the inspector to fix the pulsating problem, NOT to leave it at "Automatic".

Also, I found that if I chose a 6 GOP length, it disappeared. Don't know which of these actually fixed it, but there you go.

Now I'm dealing with a separate problem; thin green banding at the very edge of the frame of the film, but only in certain shots. I'm already bald so can't lose any more hair, but that would be happening now.