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Optimizing Video Trick-Modes Using Fast Approximations of Frame Entropy in Compressed Video Streams

IP.com Disclosure Number: IPCOM000129138D
Publication Date: 2005-Sep-28
Document File: 4 page(s) / 35K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that dynamically adjusts trick-mode engine variables based on the motion contained in the video stream, using a fast approximation of frame entropy over a sample of the video being display. Benefits include improving the fast-forward or fast-rewind of various sections of the video.

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Optimizing Video Trick-Modes Using Fast Approximations of Frame Entropy in Compressed Video Streams

Disclosed is a method that dynamically adjusts trick-mode engine variables based on the motion contained in the video stream, using a fast approximation of frame entropy over a sample of the video being display. Benefits include improving the fast-forward or fast-rewind of various sections of the video.

Background

Digital Video Recorders provide consumers the ability to watch live programming with the added benefit of enhanced “trick-modes.” Trick-modes allow the program to be paused, fast forwarded, or fast reversed. The fast forward and fast reverse modes are typically implemented by having the trick-mode engine adjust one variable, causing the video to play faster, and/or another variable causing a certain number of video frames to be skipped completely.

Exhaustive human factors testing has been conducted to determine the correct settings for each of these variables for each speed of fast forward or fast reverse. This testing revealed an unexpected finding: consumers preferred high speed, low frame skip modes at all speeds when lower-entropy video sequences were presented, but they changed their minds and preferred lower speed, high frame skip modes when higher-entropy video sequences were presented.

Current digital video recorders use a fixed set of trick-mode variables that cover the average case motion expected in a video stream. This allows for fast forward or fast reverse trick-modes, but does not provide it in the most visually pleasing way possible.

General Description

The disclosed method dynamically adjusts trick-mode engine variables based on the motion contained in the video stream, using a fast approximation of frame entropy over a sample of the video being display (see Figure 1). This allows the trick-mode engine to constantly modify variables and determine the most visually pleasing way to fast-forward or fast-rewind various sections of the video.

The disclosed method’s algorithm gives an approximation of the frame-by-frame entropy in a compressed video stream, without actually decoding the frames. This creates a frame-by-frame “signature” of the stream for characterization and categorization. This signature is used as a feedback to the trick-mode engine to adjust the frame rate and frame speed of the video playback. The disclosed method uses examples in terms of analyzing MPEG2 streams; however the concepts apply to any compression format which uses motion vectors, coded block patterns, or other entropy coding methods.

Typical entropy calculation methods involve frame analysis at the fully-decoded level. However, decoding video frames is time-consuming, and may not be a viable alternative in a fast-forward/fast-rewind environment. As part of the encoding process, a video encoder performs many different entropy-based calculations. Much of this information is extracted from the resulting bit stream without performing a...