Authored by: Jeremy J. Gustrowsky
The Federal Circuit recently reversed a Patent Trial and Appeal Board decision in a case involving U.S. Patent No. 10,225,588, which covers systems for streaming partially encrypted media content. The dispute centered on a seemingly simple question: where does a key phrase in the patent claim actually point? The answer came down to applying a well-established rule of grammar.
The patent at issue describes technology for adaptive bitrate streaming, where video quality adjusts automatically based on network conditions. To protect content from unauthorized copying, the system encrypts only portions of video frames rather than entire streams, making the process more efficient. DivX, LLC sued Netflix, Inc. for infringement, and Netflix responded by petitioning for inter partes review at the USPTO. The critical claim language required “locating encryption information that identifies encrypted portions of frames of video within the requested portions of the selected stream of protected video.”
The parties disagreed about what the phrase “within the requested portions” was modifying. DivX argued that the “encryption information” itself had to be located within the requested video portions. Netflix countered that only the “encrypted portions of frames of video” needed to be there—meaning the encryption information could be stored elsewhere, such as in a top-level index file. After a prior remand from the Federal Circuit, the Board adopted DivX’s narrower construction, finding Netflix had not proven obviousness under that reading.
The Federal Circuit reversed, relying on what linguists and lawyers call the “nearest-reasonable-referent canon” or “rule of last antecedent.” Under this principle, when a modifier could grammatically attach to more than one element in a sentence, it presumptively modifies the nearest one. Here, “within the requested portions” sits closer to “encrypted portions of frames of video” than to “encryption information,” so it should modify the former. The court found nothing in the claim language, specification, or prosecution history to overcome this presumption.
The specification actually supported Netflix’s reading. While some embodiments placed encryption information within the video stream portions, others described using a “conventional Matroska container” format that cannot hold such information—meaning it would have to be located elsewhere. A related patent from the same family even explicitly required encryption information in a “top level index file” rather than within requested stream portions. With the claim properly construed, the court found the asserted prior art taught the limitation, vacated the Board’s decision, and remanded for further proceedings.