Two-part synchronization scheme for digital video decoders

#The present invention relates generally to digital video data, and, more particularly to an apparatus and method for synchronizing a video decoder to a compressed digitized video signal.

#In the communications industry, much attention has been focused on making more effective use of the limited number of transmission channels available for delivering video information and programming to an end user. Various methodologies have been developed to achieve an increase in the number of available transmission channels within the frequency bandwidth that was previously allocated to a single video transmission channel. An increase on the number of available transmission channels would allow the communications industry to reduce costs and to increase broadcast capacity. It has been estimated that a typical cable operator could have the capability to deliver as many as 500 channels to a home viewer.

#A dramatic increase in the number of separate program channels that could be broadcast within the currently available transmission bandwidth may be realized by employing a process of compressing and decompressing video signals. Typically, the video and audio signals comprising a video program are converted into a digital format, compressed and encoded in accordance with an established compression algorithm or methodology. The compressed system signal or bitstream, which is understood to include a video portion, an audio portion, and other informational portions, may then be transmitted over existing television channels, cable television channels, satellite communication channels, and the like. A decoder is then typically employed to decompress and decode the received system signal in accordance with the same compression algorithm or methodology previously mentioned. The decoded video information may then be output to a display device, such as a television monitor.

#FIG. 1 is a block diagram of a conventional video encoding and decoding scheme;

#FIG. 2 is a block diagram representative of a conventional synchronization scheme for a digital video decoder;

#FIG. 3 is a block diagram of one embodiment of a novel two-part video synchronization scheme in accordance with one aspect of the present invention;

#Referring to the figures, and more particularly to FIG. 3, there is shown a block diagram illustrating a novel video decoding architecture in accordance with one aspect of the present invention. In a preferred embodiment, synchronization to a variable bit-rate coded signal is accomplished in a two-part process performed by a pre-parser 52 and a post-parser 56. In accordance with this aspect of the present invention, an initial multiplexed system bitstream, preferably transmitted along a fixed rate channel 50, is coupled to the pre-parser 52. The pre-parser 52 performs an initial set of operations on the bitstream which is then written to the channel buffer 54. The post-parser 56 operates on the bitstream data after reading it from the channel buffer 54.

#The pre-parser 52 performs an initial channel synchronization to the multiplexed system bitstream received from the fixed rate channel 50. Preferably, data is only written to the channel buffer 54 if the pre-parser 52 is synchronized to the bitstream. Additionally, the pre-parser 52 effectively filters the bitstream and removes unwanted digital information in the bitstream corresponding to signal components irrelevant to video image data decoding such as audio and other non-video related information. The filtered video bitstream is then temporarily stored in the channel buffer 54 to await further processing. The operations performed by the post-parser 56 and the video decoder 58 are significantly simplified since the video bitstream stored in the channel buffer 54 is already synchronized and properly aligned.

#In FIG. 4, there is shown a block diagram representative of the processes performed by the novel two-part synchronization of the present invention. Alignment, synchronization, and parsing of a multiplexed system bitstream is performed in two phases; the first by a pre-parser 52, and second by a post-parser 56. Disposed between the pre-parser 52 and the post-parser 56 is a channel buffer 54. In operation, an initial multiplexed system bitstream is input to the pre-parser 52 along a fixed rate channel 50. Within the pre-parser 52, a system stream synchronizer 62, coupled to input channel 50, synchronizes to the multiplexed system bitstream. A system stream pre-parser 63 then separates the video signal component, commonly referred to as a video bitstream, from the multiplexed system bitstream and extracts the Presentation Time Stamp. The Presentation Time Stamp is a parameter used for subsequent resynchronizing of the audio and video components.