Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output data buffering
Reexamination Certificate
1998-11-18
2001-08-07
Follansbee, John A. (Department: 2154)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output data buffering
C709S233000
Reexamination Certificate
active
06272566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to video servers and in particular to buffering short clip video streams from video servers. Still more particularly, the present invention relates to buffering sufficient video assets during video streaming from a video server to prevent interruption of video streams due to data storage device underflow.
2. Description of the Related Art
Video servers are employed in a variety of contexts for providing streams of video information. (As used herein, the terms “video information” or “video assets” are intended to encompass video, including motion, stop-motion, or frame video, and combined video/audio information). The most common utilization is for broadcasting, either over conventional electromagnetic transmission or cable. Video assets of up to 10-15 hours are stored for streaming to the broadcast device. Video servers are also beginning to be widely employed for “Web-casting,” transmission of video information over the Internet utilizing the World Wide Web format.
In video server systems, due to the nature of the underlying hardware and the real time response requirements of video streaming, it is necessary to maintain an adequate amount of video assets in short term memory buffers. Video data often originates from devices such as disk drives whose short term supply of data may fluctuate below the threshold necessary for proper streaming. For example, this can be caused by disk thermal recalibration or RAID (Redundant Array of Inexpensive Disks) data rebuild.
As a result of this data supply fluctuation, it is necessary to maintain data buffering equal to the real time streaming rate times the data storage device's maximum underflow time period. However, the device underflow time period may exceed the length of a single video clip. This easily happens with short video clips during failure of a RAID disk. In the short clip environment, it has been impossible or at least very expensive to maintain proper buffering to cover device underflow. Video streaming devices for the Internet or cable transmission typically have unique, specialized hardware solutions requiring a minimum video clip length to prevent underflow, and generally cannot handle subsecond video clips.
It would be desirable, therefore, to provide a method and apparatus for maintaining enough video data such that data storage device underflow would not result in underflow of the video decoder causing visible picture fluctuation.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved video server.
It is another object of the present invention to provide a method and apparatus for buffering short clip video streams from video servers.
It is yet another object of the present invention to provide a method and apparatus for buffering sufficient video assets during video streaming from a video server to prevent interruption of short clip video streams due to data storage device underflow.
The foregoing objects are achieved as is now described. Video assets are fetched from a data storage device and buffered based on the video rate associated with the video assets. The arrival deadline for each buffer is tracked. As the contents of a buffer are consumed by the video decoder, the buffering plan is computed. The intent of the buffering plan is to maintain enough buffering in prefetched buffers to cover a data storage device underflow. The proper amount of buffering to cover an underflow is computed by subtracting both the arrival deadline and buffer time of the next buffer to be consumed from the arrival deadline of subsequent future buffers. This computation must be performed for each future buffer until the difference is greater than or equal to the maximum storage device underflow period. If the difference is less than the storage device underflow period, then a fetch of the buffer from the data storage device must be performed. To rapidly build the buffering when the play list is first started or when device underflow substantially depletes the buffers, a higher priority I/O may be utilized.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.
REFERENCES:
patent: 5159447 (1992-10-01), Haskell et al.
patent: 5541955 (1996-07-01), Jacobsmeyer
patent: 5630067 (1997-05-01), Kindell et al.
patent: 5907363 (1999-05-01), Botsford, III et al.
patent: 5913031 (1999-06-01), Blanchard
patent: 6091776 (2000-07-01), Linzer
Bracewell & Patterson L.L.P.
Emile Volel
Follansbee John A.
International Business Machines - Corporation
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