• John Koleszar's avatar
    Reduce overshoot in 1 pass rate control · 212f6183
    John Koleszar authored
    This patch attempts to reduce the peak bitrate hit by the encoder
    when using small buffer windows.
    
    Tested on the CIF set over 200-500kbps using these settings:
    
      --buf-sz=500 --buf-initial-sz=250 --buf-optimal-sz=250 \
      --undershoot-pct=100
    
    Two pass encodes were tested at best quality. One pass encodes were
    tested only at realtime speed 4:
    
      --rt --cpu-used=-4
    
    The peak datarate (over the specified 500ms window) was measured
    for each encode, and averaged together to get metric for
    "average peak," computed as SUM(peak)/SUM(target). This patch
    reduces the average peak datarate as follows:
    
      One pass:
        baseline:   1.29715
        this patch: 1.23664
    
      Two pass:
        baseline:   1.32702
        this patch: 1.37824
    
    This change had a positive effect on our quality metrics as well:
    
      One pass CBR:
                        Min  / Mean / Max (pct)
        Average PSNR    -0.42 / 2.86 / 27.32
        Overall PSNR    -0.90 / 2.00 / 17.27
        SSIM            -0.05 / 3.95 / 37.46
    
      Two pass CBR:
                        Min  / Mean / Max (pct)
        Average PSNR    -4.47 / 4.35 / 35.99
        Overall PSNR    -3.40 / 4.18 / 36.46
        SSIM            -4.56 / 6.98 / 53.67
    
      One pass VBR:
                        Min  / Mean / Max (pct)
        Average PSNR    -5.21 /  0.01 / 3.30
        Overall PSNR    -8.10 / -0.38 / 1.21
        SSIM            -7.38 / -0.11 / 3.17
        (note: most values here were close to the mean, there were a few
         outliers on files that were very sensitive to golden frame size)
    
      Two pass VBR:
                        Min  / Mean / Max (pct)
        Average PSNR    0.00 / 0.00 / 0.00
        Overall PSNR    0.00 / 0.00 / 0.00
        SSIM            0.00 / 0.00 / 0.00
    
    Neither one pass or two pass CBR mode adheres particularly strictly
    to the short term buffer constraints, and two pass is less
    consistent, even in the baseline commit. This should be addressed
    in a later commit. This likely will hurt the quality numbers, as it
    will have to reduce the burstiness of golden frames.
    
    Aside: My work on this commit makes it clear that we need to make
    rate control modes "pluggable", where you can easily write a new
    one or work on one in isolation.
    
    Change-Id: I1ea9a48f2beedd59891f1288aabf7064956b4716
    212f6183
onyx_if.c 166 KB