As a general rule, the words "a" or "an" in a patent claim carry the meaning of "one or more." Baldwin Graphic Sys., Inc. v. Siebert, Inc., No. 2007-1262, slip op. at 7 (Fed. Cir. Jan. 15, 2008). That is particularly true when those words are used in vombination with the open-ended ntecedent "comprising." See, e.g., Abtox, Inc. v. Exitron Corp., 122 F.3d 1019, 1023 (Fed. Cir. 1997). However, the question whether "a" or "an" is treated as singular or plural depends heavily on the context of its use. See Norian Corp. v. Stryker Corp., 432 F.3d 1356, 1359 (Fed. Cir. 2005). The general rule does not apply when the context clearly evidences that the usage is limited to the singular. Baldwin Graphic, slip op. at 10.Unlike the case in Baldwin Graphic, where the claims and the written description could be read to encompass either a singular or plural interpretation of "a" or "an," the claims and written description in this case make clear that the singular meaning applies. The pertinent claim language refers to "assembl[ing] said video and audio components into an MPEG stream," which in context clearly indicates that two separate components are assembled into a single stream, not that the video components are assembled into one stream and the audio components into a second stream. Earlier limitations in the claims refer to converting specific programs into an MPEG stream, parsing that MPEG stream and separating it "into its video and audio components." Later limitations refer to sending the reassembled MPEG stream to a decoder and converting it into TV output signals. Those steps clearly describe theseparation of a single stream into two components and then reassembly of the components into a single stream for conversion into television signals. Moreover, although the open-ended term "comprising" is used to refer generally to the limitations of the hardware claims, the "assembles" limitation itself does not contain that term. Rather, the claim language simply refers to the assembly of two components into "an MPEG stream."
The corresponding explanation in the specification refers to separating the MPEG stream into video and audio components, which are then "reassembled into an MPEG stream." ’389 patent, col. 2, ll. 15-29. That language describes the process of separating one stream into two sets of components and then reassembling the two sets of components into a single stream. In particular, when discussing the term "assembles," the specification states that "when the program is requested for display, the video and audio components are extracted from the storage device and reassembled into an MPEG stream which is sent to a decoder. The decoder converts the MPEG stream into TV output signals and delivers the TV output signals to a TV receiver." ’389 patent, Abstract; id., col. 2, ll. 27-32. The specification also provides that the "MPEG stream has interleaved video . . . and audio . . . segments." Id., col. 4, ll. 23-26. That language, like the claim language, describes the MPEG stream that is "reassembled" as a single MPEG stream, not two different streams. The concept of reassembly indicates that the MPEG stream is restored to an earlier state, which in this case would be the state in which it was initially received by the system, as a single stream of data. Accordingly, we agree with EchoStar that the claim would be interpreted by one having ordinary skill in the art to require the reassembly of the audio and video components into a single interleaved stream.