Prefer Quality over Frame Rate

Prefer Quality over Frame Rate

Upon being encoded, each frame is given a quality score, based on how much compression was required to encode the frame to the available bitrate -- essentially, how blocky was each encoded image. The Prefer Quality over Frame Rate setting allows you to specify a specific threshold for the video codec's quality score to reach before dropping frames to preserve a given video quality level.

If the resolution or framerate was comparatively too high for the max bitrate setting, then the score will be worse than the same frame compressed at a higher bitrate. The scores for each frame range from 0 (best possible score) to 300 (worst). Though quality should be judged by the user, typically frames that score lower (better) than around 40-60 are adequate for broadcast. These scores can be seen on the Encoder statistics display; one value shows the instantaneous value for the current frame (and changes rapidly) while the second value is an average over a number of seconds.

Prefer Quality over Frame Rate has two settings: The "I-Frame" (keyframe) value (intra frame / keyframe) represents the quality threshold of a new full frame. The "P/B-Frame" (delta frame) (predicted frame / bi-directional interpolated frame) value represents the quality of predicted frames. Both settings allow for a setting of 0 to 300.

A typical use of Prefer Quality over Frame Rate would use a setting of 300 for I-Frames (so no i-frame/keyframe is ever dropped) and around 40 for the delta frames. Most users of Prefer Quality over Frame Rate are streaming at low or very low bitrates, below 500kbps. This setting is also preferred in security applications, where high-quality video frames are more important than high frame rate.

NOTE: When using Prefer Quality over Frame Rate, you must use either a progressive video source format (such as 720p, 1080psf, or CIF), or select the De-Interlace filter on the encoder, in order to avoid interlace artifacts.