bitrate artifact at every key frame with VP8

[GoogleCodeExporter]

Trying to encode video with a single static image leads to artifacts at every 
key frames.

Attached is the tests/lena.pnm test picture from FFmpeg. To get a 500 frames 
(20sec @ 25fps) video input stream with it:

  ffmpeg -loop 1 -i lena.pnm -vf 'scale=2*iw:2*ih' -pix_fmt yuv420p -t 20 -y /tmp/in.y4m

Encoding with vpxenc:

  vpxenc /tmp/in.y4m --codec=vp8 --target-bitrate=200 --fps=25/1 --best --cpu-used=0 -o out.webm

Play the file and wait for a key frame (5, 10 or 15 seconds). You should 
observe a violent blurring artifact.

The issue is less visible with a high bitrate, but still observable.

Reproducible with v1.3.0 and v1.3.0-1495-gaf7d997.

This bug is extremely annoying when typically recording a terminal session; 
terminal text gets suddenly blurry at every key frame.

Not tested with VP9.

Original issue reported on code.google.com by ubi...@gmail.com on 27 Feb 2014 at 8:32

Attachments:

• lena.pnm

[GoogleCodeExporter]

Original comment by ya...@google.com on 27 Feb 2014 at 11:18

• Changed state: Assigned

[GoogleCodeExporter]

I suggest you to lower your --max-q and increase --max-intra-rate

The first one control the worst frame quality with valid input [0, 63], the 
second one is a percentage number allowing a key frame to use at most x% of 
bandwidth. There is no limit to the second option, you might try really large 
ones to test. For example, starting 10000 to see if you see any difference. 

we would appreciate if  you report back your findings or open a new bug. 

Original comment by ya...@google.com on 4 Apr 2014 at 1:13

• Changed state: Done