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Tutorial: Using Windows Media Registry Keys

Dquant Option
Dquant is short for differential quantization. It applies a form of perceptual optimization where it varies the amount of compression on different parts of the frame. This can help video quality, especially where there might be blockiness in textured areas or gradients. The drawback to Dquant is that it can apply a lot of bits to those textured areas, reducing bits available to other parts of the image.

The default is off, but the Compression Optimization Type 1 sets it to be I- and P-Frame only. This is a good compromise for most content, since the B-Frames can be based on the Dquanted frames, but don’t spend the bits on themselves. A value of 0 sets the Dquant to off; 1 applies it to the I-Frame only; 2 to the I- and P-Frames, and 3 to the I-, P-, and B-Frames.

Denoise Option
Denoise is a built-in noise reduction filter. It can help a lot with noisy sources, like with prominent film grain or video shot in low light. It should be left off for clean sources, since it increases encoding time, and can overly soften clean video.

Loop Filter
Loop Filter is short for in-loop deblocking filter. Deblocking is a technique for reducing the appearance of blocky artifacts in the video. Traditional deblocking has been a purely postprocessing step, but didn’t change the underlying data. In-loop deblocking is a recent innovation that reduces the blocking artifacts internally to the codec so that future frames don’t carry forward the blocking artifacts.

Using the loop filter can soften the image slightly, but can dramatically improve video quality at low-to-moderate data rates. The biggest concern with using the Loop Filter is that it can slow decoding significantly; most other features only affect encoder performance. It’s not a big deal with 320x240 on a modern machine, but test carefully if targeting older hardware and higher resolutions.

Force Median
The Windows Media Force Median control operates differently from the Median blur filter found in tools like Adobe Premiere Pro and Canopus ProCoder. It tells the codec to ignore noise and grain when calculating motion from frame to frame. It can improve the quality of very noisy video, but shouldn’t be used with most other content—it can leave "trails" in the video, and it also slows down encoding.

Force Noise Edge Removal
Force Noise Edge Removal is a special-purpose filter, but it can be enormously useful. It simply blanks out video noise around the edges of the screen that wouldn’t be seen on a television, but can appear in a web video window. It should only be used if the source has noisy edges.

Force Overlap
The Force Overlap filter controls what happens when an area has regions that include different parts of other frames. Overlap smoothing tends to make the image softer, but can reduce artifacts with complex, low bit rate video. It should be used on a case-by-case basis when a loss of detail is preferable to artifacts.

The Lookahead parameter is a great new feature for live encoding. Only used in the single-pass CBR mode, it lets the codec partially encode a frame, but not make the final decision on its bit rate until the specified number of frames have passed. So, with the maximum value of 16, the codec is able to know what the next 16 frames look like before deciding what data rate to give a given frame. This lets it adapt to take advantage of simpler frames coming up, or save bits to spend on more complex frames.

Lookahead does increase encoder complexity a little, but it’s well worth it. I recommend you use the full value of 16, though you can select any value between 0 and 16. Note that the current Lookahead implementation adaptively adjusts B-Frame placement based on the content. This means Lookahead should not be used for Simple Profile encoding, since it can insert B-Frames even if NumBFrames equals 0.

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