[MPlayer-users] Horrible Compression Artifacts in High MotionScenes

[Loren Merritt]

On Mon, 3 Oct 2005, Nico Sabbi wrote:
> Kichigai Mentat wrote:
>
>> Hello. I'm attempting to compress a video with the following command  line:
>> 
>> mencoder INPUT -o OUTPUT -nosound -ovc lavc -lavcopts vcodec=mpeg4:vpass=3:
>> aspect=16/9:idct=8:trell:vmax_b_frames=0:vqmax=31:vhq:v4mv:vrc_eq=tex:vfdct=5:
>> dia=-1:vbitrate=1200:vrc_minrate=650:vrc_maxrate=2500:vrc_buf_size=1835
>> -vf crop=720:464:0:8,filmdint=dint_thres=256,pp=lb -ofps 29.976
>>
>> My guess was with that kind of a bitrate, there would be enough 
>> information to compensate for high-motion scenes (which this video is  full 
>> of). Instead, the result was that virtually all high-motion  scenes are 
>> flooded with compression artifacts. Scenes with repetitive  motion (the 
>> same background repeating) or even as simple as following  someone running 
>> comes out with blocking everywhere. Low motion scenes  are crystal clear, 
>> but high-motion scenes (which make up the bulk of  the video) do not, even 
>> after three or four passes. Any ideas on  what's going on, or how to fix 
>> it?

vbitrate=1200 might be enough, but vrc_maxrate=2500 is way too small, and 
setting vrc_minrate to anything at all just wastes bits.

> my advice is to add :sc_threshold=N (usually I use -1500) to enable lavc's 
> scene change detection

"enable"? scene change detection is on by default, you're just somewhat 
increasing the number of keyframes.

--Loren Merritt