DVD Studio Pro Artifacts with VBR on clips over 12min

S

sublimesnfu

Well-known member
Hello I am posting this for a friend. I have included links to two example clips below. Any help would be greatly appreciated.


The source video is uncompressed 8 bit 4:2:2 yuv and edited in the same codec. When the timeline is sent to Compressor using a CBR encoding profile, the dvd assets render correctly. If I use a VBR - 2 pass, Best Motion profile, any encoding after ~ 15 minutes displays the "pulsing" of mosquito noise effect. The same assets VBR encoded on an older MAC system using the Quicktime MPEG - 2 exporter or Adobe's Media Encoder does not have this problem.


http://vimeo.com/13049361
http://vimeo.com/13049370

Thanks
Alan
 
Examining the streams now, it seems odd that the quality *decreases* on the I-frames... Usually, sudden bitrate pumping is seen in the form of *increases* in quality on I-Frames, but you have the opposite going on here. Also, this is just semantics, but it's not mosquito effect, it's full macroblocking at its "finest".

I suspect this is a rate control issue with the encoder, but what I do know is that the bitrate is far too low for MPEG-2 SD material. I would bump this to around 7Mbits, maybe 6.5, but you've capped it at about 4.5 it seems, which is terribly low. I've never had this problem with DVD SP in the past, but I've also never pushed my bitrate so low. My only guess is that because of its average bitrate being essentially the same as its max bitrate, the encoder cannot fully create the I-Frame, so it becomes bit-starved.

Again, shoot for 7Mbit average, 8.5 Mbit maximum. (These are separate settings)
 
sublimesnfu - Thanks for the response... I thought the same thing, however I have encoded that material at the highest bitrate and still experienced the artifacting. Also as I stated, this did not occur using the old MPEG2 export from QT function on another MAC as well as Adobe's Media encoder. Since the final project is over 2 hours, the bitrate must be set lower like Hollywood titles.
 
RX782 is correct, the I-frames are not allocated enough bitrate, which is usually the opposite case

I'm not a MAC user, but see if there are some settings for I:P ratio or P:B ratio adjustment

The metadata says "Womble" ; did you cut those sample videos with Womble?

Why not use another encoder?
 
When you need to encode a 2hour feature to fit on a DVD, you really need a high quality Pro encoder that can do auto GOP placement, meaning that I frames are placed when its needed. it's what allows you to go into the 6Mbps bitrates and still look good.

HCENC supports this and is freeware. Some higher end compressors like Mainconcept and Episode Pro support this feature as well, but you'll pay for it.

Last I checked, Premiere Pro nor Compressor support auto GOP placement. It fixes it to a certain rate, and always looks bad when you drop the bitrate.
 
I think part of the point my friend was trying to make was that this never happened with the old DVD compression method using QT.
 
You must log in or register to reply here.
Back
Top