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A portion of the disclosure of this patent document, which may include copyrighted images, contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a non-provisional of U.S. Provisional Patent Application No. 62/875,250, filed on Jul. 17, 2019 entitled “VIDEO FRAME PULLDOWN BASED ON FRAME ANALYSIS.” The entirety of the aforementioned application is hereby incorporated herein by reference.

BACKGROUND

Frame pulldown (sometimes identified with two words, “pull down”) refers to “stretching” a video by inserting new frames into the video, such as to convert groups of four frames of video into five frames. By way of example, consider a film recorded at 23.976 frames per second (often referred to as 24 frames per second). In the United States and other countries where television uses a 59.94 Hz vertical scanning frequency, video is broadcast at 29.97 frames per second (often referred to as 30 frames per second). For the film's motion to be accurately rendered on the video signal, a pulldown process is used to convert from the source's 24 frames per second to the needed 30 frames per second.

One way to perform pulldown is to repeat a field from every other frame, referred to as 2:3 (or 2-3) pulldown. Consider for example four frames A, B, C and D, which are divided into two fields each, providing AA, BB, CC, and DD. When creating a five frame sequence, the second and fourth frames can each have a repeated field, such that the fields are AA B B B C C D D D, which then make fields AA BB BC CD and DD. Note that by repeating fields of the first and third frames instead of the second and fourth, this can be alternatively arranged as A AA B B C C C D D, referred to as 3:2 (or 3-2) pulldown. This process repeats, whereby 24 frames per second can be displayed as 30 frames per second. Note that the actual frame rate used is 29.97 frames per second, which is a legacy carryover from television going to color and avoiding a problem with television broadcast sound subcarrier.

Video that has been converted with conventional pulldown often suffers from undesirable visible effects such as judder. At the same time, with video streaming, while it is possible to stream video at 24 frames per second and avoid pulldown, 30 frames per second provides a much better viewing experience for streams that play fast motion, such as streamed sporting events. Note that the frame rate for a linear feed needs to remain constant, and, for example, cannot be dynamically changed from 30 frames per second to 24 frames per second back to 30 frames per second.

