Magix Mainconcept AVC render quality problem

EricLNZ wrote on 5/24/2019, 6:08 AM

I've stumbled across a problem with the Mainconcept Blu-ray renders in the MAGIX AVC/AAC MP4 templates.

Using the Magix AVC/AAC Blu-ray 1920x1080-50i, 25 Mbps video stream template with 1 pass VBR and the only change being reducing the max bitrate to 35,000,000 (DVDA recompresses if you use 40,000,000 as reported elsewhere) I get noticeable edge shadow when objects move against a clear background. I'm using the Mainconcept AVC Encode mode CPU processing only. This is visible when I play the avc file in MPC-HC player and advance frame by frame, or drag the file into a VMS 50p timeline and advance frame by frame. The shadow, similar to a drop shadow, moves alternatively from behind the object to in front of it. I took the avc file through to a m2ts file in a Blu-ray iso image using DVDA and the problem still existed.

Rendering with the similar old Mainconcept template (enabled via preferences) does not give the problem nor does rendering with Sony AVC. So it is perculiar to the new render template.

Two images attached to try and show the problem. The cyan is moving across covering the red and should have a clean edge. It does in the original Mainconcept but doesn't in the Magix Mainconcept .

Santa on his sleigh is chasing the title off the screen. Unfortunately the image may not be large enough to clearly show the edging.

I've also noticed it with occasional shots from my camera. For example a red banner moving against a grey sky. The banner had edging like the red colour had bled.

I'd be grateful if someone could check my findings with a simple project .

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Comments

nepomuk wrote on 5/26/2019, 1:32 PM

Conversion of progressive material to true interlaced is not simple, because the missing field has basically to be generated in some way. There exist various approaches, like
- separate the progressive source frames into odd an even (virtual) fields, which in this case have no temporal difference, then encode and flag as interlaced. This will satisfy authoring tools and players which expect an interlaced format, but of course the temporal resolution is the same as the source. It is sometimes referred to as "fake interlaced" as the underlying material is progressive.
- Generate the missing field by blending adjacent frames and use the blends as "in between new frames" (or fields). This seems to be what MAGIX MC now does in VMS 16.
- Synthesize the missing field by temporal interpolating rather than just use blending. I have some doubts that VMS 16 does this properly. It should not produce blends or shadows, but is prone to other artifacts.

Unfortunately the documentation of VMS is not clear what happens under the hood, but what happens is definitely different when we render with Draft/Preview.... or Best quality.

Maybe I am missing something and someone else can shed some light on it.

EricLNZ wrote on 5/28/2019, 3:03 AM

I've now rendered my videos, that were unsatisfactory with the Magix MainConcept Blu-ray codec, with the original MainConcept Blu-ray codec. Using the same VBR 1 pass max bitrate 35 Mbps, Average 25 MBPS I find:

The files produced by the original codec are usually larger by up to 17%. Unfortunately MediaInfo only tells me the bitrate is max 35 and variable. It doesn't indicate the average so I cannot compare.

The Magix MC files correctly indicate they are Standard PAL. The original MC files say they are Standard NTSC even though they are correctly 50i Top field first. Presumably this won't cause me problems with DVDA. It is accepting them without recompression although I haven't created a disk image with them as yet.

nepomuk wrote on 5/29/2019, 2:11 PM

I am confused now. Are your videos frame rate converted by any of the encoders, like from 50i (PAL) to 29.97i (NTSC) or vice versa? Or do the old MC and MAGIX MC just report the same source differently?

EricLNZ wrote on 5/29/2019, 7:13 PM

I am confused now. Are your videos frame rate converted by any of the encoders, like from 50i (PAL) to 29.97i (NTSC) or vice versa? Or do the old MC and MAGIX MC just report the same source differently?

No, nothing is changed. Attached is MediaInfo for the two files and as you can see they are otherwise identical apart from a difference in file size. The original MC being larger. Unfortunately MediaInfo doesn't report the average bitrate to compare the difference They should be 25 Mbps average. Both correctly show Max 35.00 Mbps which is what I set them to as the template 40 gives problems with DVDA. This was the subject of a thread here.

The video is 5 Mins 19 Secs long i.e. 319 Secs. That gives average bitrates of 28.14 Mbps for the original MC and 24.29 Mbps for MagixMC. So the Magix MC is closer to the requested 25 Mbps average. As a test I also did a 1 minute render using 20 Mbps CBR with each. The file sizes were close (147,233 KB for original MC and 147,374 KB for Magix MC).

EricLNZ wrote on 5/7/2020, 3:52 AM

This problem with rendering Blu-ray AVC files with the Magix MainConcept codec has been fixed with VMS17 Platinum Build 143. At least for me.