Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-07-06
2001-02-27
Kelley, Chris S. (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06195393
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for processing a sequence of video or other data frames at a data encoder during a synchronization (“sync”) loss. When a sync loss is detected, black or pre-stored frames are provided in sync with the pre-sync loss frames until re-synchronization has been established. Null data is provided if necessary when the post-sync loss frames are not synchronized with the pre-sync loss frames. The invention is particularly suitable for use with a digital video encoder that encodes High-Definition Television (HDTV).
The communication of digital video, audio, and other data has become increasingly common due to the improved fidelity, bandwidth efficiency, and versatility of digital signals relative to analog signals. For example, many cable television (CATV) networks deliver digital television signals to users' homes via coaxial cable, or hybrid fiber and coaxial cable networks. Moreover, in addition to television signals, various other signals may be provided to the user, including audio only, video only, including still frame video, as well as data services, including Internet data, stock or weather data, computer games, and so forth.
The television or other data is transmitted from a headend of the cable network to a decoder at the user's home, or directly to the user's home, e.g., via satellite or terrestrial broadcast, and processed by the decoder to provide an output signal having a format that is compatible with the user's television, computer or other equipment.
The television or other data may be obtained by the headend via various methods. For example, the headend may have a local library of digital television programs or other data which is stored on magnetic storage media such as magnetic tape, or optical storage media, such as compact disc, digital video disc, or laser disc. The headend may also receive digital television or other data from a transmission source, including, for example, a satellite distribution network, a terrestrial broadcast network, or a microwave distribution network.
Each frame in a video or other data signal includes timing, or clock, information that allow a video encoder to be synchronized with the signal to allow proper compression and encoding. It is problematic that a sync loss may be experienced at the video encoder due to a number of factors. For example, a change in data source, e.g., from a live television broadcast to a pre-recorded movie, may result in a sync loss, thereby causing undesirable visible or other artifacts in the transmitted data stream. Additionally, a data dropout due to a defect in a data storage medium or noise in a transmission channel may result in a sync loss.
Furthermore, a change in data source may be accompanied by a change in video clock rate. For example, the HDTV format of 1920 horizontal pixels×1080 active video lines×30 fields per second interlaced scan (e.g., 540 active video lines per field) has a clock at 74.25 MHz, while the format of 1920 horizontal pixels×1080 active video lines×29.97 fields per second interlaced scan (e.g., 540 active video lines per field) has a clock at 74.175 MHz. These HDTV formats are discussed in the document SMPTE 274M, entitled “Proposed SMPTE Standard for Television−1920×1080 Scanning and Analog and Parallel Digital Interfaces for Multiple-Picture Rates.” It is difficult for the encoder to re-synchronize with the new video clock.
Additionally, a data buffer which receives the input data signal may overflow during a sync loss since no encoding and transmission of the received data occurs.
Accordingly, it would be desirable to provide a system for processing a sequence of video or other data frames which are input to a data encoder/compressor during a sync loss. The system should provide substitute data, such as black or pre-stored data, to a data compressor that are synchronized with the pre-sync loss data frames until synchronization is re-established. For example, for frames of video data, black frames may be provided to the compressor.
The system should accommodate a change in clock rate of the post-sync loss frames relative to the pre-sync loss frames.
The system should further accommodate post-sync loss frames which are either synchronous or asynchronous with the pre-sync loss frames.
The system should provide a null signal to the compressor, if required, during a period following the establishment of resynchronization and prior to communication of a new data frame to the compressor.
The system should manage a buffer fullness level in the data encoder to prevent overflow during a sync loss.
The present invention provides a system having the above and other advantages.
SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for processing a sequence of video or other data frames at a data encoder during a sync loss.
During a sync loss of input data at a video or other data encoder, the present invention provides only complete data frames to a compressor at the encoder by generating substitute data as required. By providing only complete data frames, undesirable data artifacts are avoided. Sync loss may occurs when the encoder's data source is switched.
For example, if a sync loss is detected in the middle of a particular data frame that is input to the encoder, the remainder of the frame is completed with substitute data which is in sync with the earlier data in the frame. Additionally, complete “clean” frames of the substitute data are provided to the compressor following the particular data frame, still in sync with the particular frame, until a sync recovery is detected, and a field or frame check is performed on the new, post-sync loss, data to gain confidence of the sync recovery.
If the post-sync loss data is not in sync with the pre-sync loss data (i.e., there is a different time base), it may be necessary to provide a null signal to the compressor after the last substitute frame, and prior to the post-sync loss frame after the frame in which a field or frame check occurs. This post-sync loss frame is referred to as a post-check frame. Different frame and video clock rates in the post-versus pre-sync loss frames are automatically accounted for.
In accordance with the present invention, a method for processing frames of data that are input to a data encoder when a loss of synchronization between the input data frames and the encoder is detected, includes the steps of: monitoring the input data frames to detect a sync loss; providing pre-sync loss input data of the input data frames to a data compressor of the encoder prior to detection of the sync loss; and providing substitute data to the data compressor in synchronism with the pre-sync loss input data when the sync loss is detected.
The input data frames continue to be monitored to detect a sync recovery; and the post-sync loss input data of the input data frames is provided to the data compressor after the sync recovery is detected, and after a last frame including the substitute data is provided to the data compressor.
The input data frames may include video data, in which case the substitute data may include black video data, which is generated real-time as needed.
The substitute data may be pre-stored in a memory. For example, the last pre-sync loss frame may be pre-stored and communicated to the compressor. For a video application, this would allow the viewer to see the last good video frame, for example, or some other default video frame, rather than a black screen. However, additional memory is required.
Sync loss may be detected by monitoring start of active video (SAV) and/or end of active video (EAV) fields of video lines of the pre-sync loss input data.
The method may include the step of monitoring an input clock signal that is associated with the pre-sync loss input data to detect the sync loss.
A first complete frame that includes the pre-sync loss input data and the substitute data may be provided to the data compressor when the sync loss o
Kaku Vicky B.
Nemiroff Robert
General Instrument Corporation
Kelley Chris S.
Lipsitz Barry R.
Philippe Gims
LandOfFree
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