x264 purple artifacts

[giandrea]

Hello! I was encoding a small clip with x264 through ffmpeg and in the encoded video there are some strange purple artifacts. I used the following command with ffmpeg:

ffmpeg -i input_file.mpg -croptop 70 -cropbottom 70 -cropright 4 -cropleft 4 -s 640x272 -aspect 2.3225 -ss 21 -vcodec h264 -ab 128 -rc_eq 'blurCplx^(1-qComp)' -level 30 -b 1000k -qmin 16 -subq 6 -sc_threshold 40 -partp8x8 -partb8x8 -parti4x4 -partp4x4 -maxrate 1500k -me umh -me_range 12 -vframes 1000 -pass 1 output_file.mp4

The option that triggers the artifacts is -partp8x8.

I compiled x264 and ffmpeg from the latest svn on MacOS X PPC.
Can it be related to the altivec optimization? just wondering...

You can see the artifacts in this clip:
http://www.motoriweb.com/public/test_amelie.mp4 (http://www.motoriweb.com/public/test_amelie.mp4) (~1MiB)

Thank you,

Andrea Gianarro

[bond]

does this happen with all decoders? which ones did you try?

are you sure this isnt already there when decoding the source?

[giandrea]

does this happen with all decoders? which ones did you try?

are you sure this isnt already there when decoding the source?


Yes, I'm sure, because removing the -partp8x8 options, removes the artifacts.
And I decoded it with QuickTime and MPlayer, and they both show the same artifacts. You can test by yourself anyway. :)
bya,

giandrea

[giandrea]

Yes, I'm sure, because removing the -partp8x8 options, removes the artifacts.

OK, keeping partp8x8 and lowering the bitrate works. This sounds really strange, and perhaps it is because of some parameter set to a weird value by default by ffmpeg...

Well, lowering the bitrate to 500kbps removes many purple blocks, but not all. Lowering to 200kbps removes all purple blocks... very very strange... It seems that the purple blocks appear at very low quantizers... but I don't have the means to prove this... can someone run x264 --visualize on my test clip? Thanks!!