H.264 flashing motion artifacts on scene changes

[adramolek]

I'm experimenting with HandBrake (Windows) trying to encode some cartoons at as low a bit rate as possible (so I can put them on a mobile device with limited space). It's looking good so far except I'm getting some strange artifacts on scene changes, which I can only assume are some kind of motion estimation artifacts. Here is a sample frame (I've added the blue border for contrast, the dithering is just the PNG image I posted -- not part of the video):



The artifacts are the white blotches at the bottom. It looks like the background showing through behind blocks. That white strip appears for exactly 1 frame just before a scene change in the cartoon. Sometimes it appears on the top as well -- just depends on the content.

Here are the settings I am using in HandBrake:

 -i "input.mkv" -t 1 -c 1 -o "output.mp4" -f mp4 --strict-anamorphic  --denoise="strong" -e x264 -b 190 -2  -T  -a 1 -E faac -6 stereo -R 44.1 -B 96 -D 0 -x me=umh:bframes=16:subq=9:8x8dct=1:mixed-refs=1:b-adapt=2:direct=auto:merange=64:analyse=all:deblock=1,1:no-fast-pskip=1:trellis=2:psy-rd=1.0,1.0:ref=4 -v 1

Size: 640x480 @ 4:3 (input and output same size)
Input Denoise: Strong
Codec: H.264
FPS: Same as source (it's 24)
2-pass encoding + turbo first pass
Average Bitrate: 190 kbps

Reference Frames: 4
Mixed References: Yes
B-Frames: 16
Adaptive B-Frames: Optimal
Direct Prediction: Automatic
Weighted B-Frames: Yes
Pyramidal B-Frames: No
Motion Estimation Method: Uneven Multi-Hexagon
Subpixel Motion Estimation: 9
Motion Estimation Range: 64
Analysis: All, 8x8 DCT
Entropy Coding: CABAC, Trellis=2
Psychovisual Rate Distortion: 1.0
Psychovisual Trellis: 1.0
No Fast P-Skip: Yes
No DCT-Decimate: No
Deblocking: 1,1

It has taken me a while to arrive at those settings, and I never noticed the artifact because it was very quick, and didn't show up well in the sections I was previewing.

I will be tweaking the settings to find the troublesome one tonight (I've been procrastinating too long ), but I'm also posting here before I do that because it is tedious (the previews take a while to generate) and I'm wondering if anybody has some input that could save me some trouble.

Does anybody know what is causing that and how I can stop/minimize it? I have a hunch it's a combination of high motion estimation range + multiple reference frames... but I haven't had a chance to try tweaking those settings yet.

Thanks!
M

[poisondeathray]

Input Denoise: Strong

It might be from handbrake's denoiser - maybe it's scene detection isn't up to par

Your ME range is overkill for SD content, even on HD content with "placebo" settings it's 24 .

[intracube]

The artifacts are the white blotches at the bottom. It looks like the background showing through behind blocks. That white strip appears for exactly 1 frame just before a scene change in the cartoon. Sometimes it appears on the top as well -- just depends on the content.

Does anybody know what is causing that and how I can stop/minimize it?

This might sound like a stupid question, but are you sure the artifacts aren't on the original video clips? It doesn't look like typical digital artifacts.

It looks a bit like damage caused to the original film negative where it was cut and spliced together - which is usually hidden by the overscan of most TVs. Although, if it's a recently made cartoon, my crazy theory is less likely.

[adramolek]

This might sound like a stupid question, but are you sure the artifacts aren't on the original video clips? It doesn't look like typical digital artifacts.

It looks a bit like damage caused to the original film negative where it was cut and spliced together - which is usually hidden by the overscan of most TVs. Although, if it's a recently made cartoon, my crazy theory is less likely.

Hey, well what do you know, it looks you hit the nail right on the head! I just checked the original and lo and behold, there it is. Duh...

It's not an old cartoon, but it's not new either, it's from 1997. It's a rip off of my DVDs, which I've only ever watched on my old TV, and just like you said, it's cut off the TV (I just watched it now on the TV to check).

Well that was easy, and I feel a little stupid, haha. Thank you!

@poisondeathray: Thanks for the tip; I lowered it to 20 and didn't notice much size change with constant quality. There are some very fast moving scenes in this cartoon, background stills being quickly panned, so I thought the high range might help squeeze out a little more quality here and there, but it doesn't actually seem to make much difference at all. I guess things would have to move pretty fast -- 64 pixels at 24 fps means it would be moving across the screen in under a half a second, which is way faster than the scenes I am thinking of, and saving a couple of bits over a half a second in a 23 minute video doesn't really have much of an impact on the remaining parts anyways.


Thanks guys!

[intracube]

It's not an old cartoon, but it's not new either, it's from 1997. It's a rip off of my DVDs, which I've only ever watched on my old TV, and just like you said, it's cut off the TV (I just watched it now on the TV to check).

Anamorphic 35mm films occasionally show artifacts near the top or bottom of the frame at edit points. It usually looks like a discolouration/gradient running the full width of the image.

I think due to the usable frame area having smaller margins between adjacent frames compared with other film formats.

As films are edited digitally these days, it's not an issue.