Method of processing a sequence of coded video frames

A method of modifying a digital data stream composed of a sequence of frames, where each frame represents an image and includes a data field specifying a presentation time stamp value for the frame, comprising:

• a. initializing a frame interval variable (Int_fr) with a frame interval value based on a nominal frame rate;
• b. receiving a first frame and reading the presentation time stamp value of the frame, assigning the presentation time stamp value of the first frame to a presentation time stamp variable (PTS), assigning a value of PTS to a clock start variable (Clock_start) for representing the first frame's clock time based on presentation time stamp, assigning a value of PTS to a clock presentation time stamp variable (Clock_pts) for representing a frame's clock time based on presentation time stamp, and assigning a value of zero to a stream time stamp variable (ST*) for representing a stream time stamp of interest;
• c. receiving a next frame and reading the presentation time stamp value of said next frame, assigning the presentation time stamp value of said next frame to PTS, assigning the updated value of PTS to the variable Clock_pts, and assigning a value (ST*+Int_fr) to the variable ST*;
• and
• d. testing whether there is a discontinuity in presentation time stamp value between said next frame and the previous frame and, if so, assigning the updated value of ST* to a second stream time stamp variable (ST_dis*) for representing the value of the stream time stamp of interest at a point of discontinuity in presentation time stamp and assigning the value of PTS to the variable Clock_start and storing said next frame in a database using the value of ST* as an index.

A video recording device for recording a sequence of coded video frames conveyed by a digital data stream, where each frame represents an image, the video recording device having an input terminal for receiving the digital data stream and comprising a computing machine programmed to perform the steps of:

• a. determining a frame interval between presentation of an ith coded frame of the sequence and an (i+l)th coded frame of the sequence,
• b. calculating a stream time stamp for the ith coded frame, wherein the calculated stream time stamp increases monotonically throughout the sequence of coded video frames as it is recorded, and
• c. calculating a stream time stamp for the (i+1)th coded video frame based on the stream time stamp for the ith coded video frame and the frame interval determined in step b;
• the steps further comprising:
• d. initializing a frame interval variable (Int_fr) with a frame interval value based on a nominal frame rate;
• e. receiving a first frame and reading the presentation time stamp value of the frame, assigning the presentation time stamp value of the first frame to a presentation time stamp variable (PTS), assigning a value of PTS to a clock start variable (Clock_start) for representing the first frame's clock time based on presentation time stamp, assigning a value of PTS to a clock presentation time stamp variable (Clock_pts) for representing a frame's clock time based on presentation time stamp, and assigning a value of zero to a stream time stamp variable (ST*) for representing a stream time stamp of interest;
• f. receiving a next frame and reading the presentation time stamp value of said next frame, assigning the presentation time stamp value of said next frame to PTS, assigning the updated value of PTS to the variable Clock_pts, and assigning a value (ST*+Int_fr) to the variable ST*;
• and
• g. testing whether there is a discontinuity in presentation time stamp value between said next frame and the previous frame and, if so, assigning the updated value of ST* to a second stream time stamp variable (ST_dis*) for representing the value of the stream time stamp of interest at a point of discontinuity in presentation time stamp and assigning the value of PTS to the variable Clock_start and storing said next frame in a database using the value of ST* as an index.

A non-transitory computer-readable storage medium containing software which, when read and executed by a computing machine receiving a sequence of coded video frames conveyed by a digital data stream, where each frame represents an image, causes the computing machine to perform a method for recording the sequence, the method comprising:

• a. determining a frame interval between presentation of an ith coded frame of the sequence and an (i+1)th coded frame of the sequence,
• b. calculating a stream time stamp for the ith coded frame, wherein the calculated stream time stamp increases monotonically throughout the sequence of coded video frames as it is recorded, and
• c. calculating a stream time stamp for the (i+1)th coded video frame based on the stream time stamp for the ith coded video frame and the frame interval determined in step a;
• the method further comprising:
• d. initializing a frame interval variable (Int_fr) with a frame interval value based on a nominal frame rate;
• e. receiving a first frame and reading the presentation time stamp value of the frame, assigning the presentation time stamp value of the first frame to a presentation time stamp variable (PTS), assigning a value of PTS to a clock start variable (Clock_start) for representing the first frame's clock time based on presentation time stamp, assigning a value of PTS to a clock presentation time stamp variable (Clock_pts) for representing a frame's clock time based on presentation time stamp, and assigning a value of zero to a stream time stamp variable (ST*) for representing a stream time stamp of interest;
• f. receiving a next frame and reading the presentation time stamp value of said next frame, assigning the presentation time stamp value of said next frame to PTS, assigning the updated value of PTS to the variable Clock_pts, and assigning a value (ST*+Int_fr) to the variable ST*;
• and
• g. testing whether there is a discontinuity in presentation time stamp value between said next frame and the previous frame and, if so, assigning the updated value of ST* to a second stream time stamp variable (ST_dis*) for representing the value of the stream time stamp of interest at a point of discontinuity in presentation time stamp and assigning the value of PTS to the variable Clock_start and storing said next frame in a database using the value of ST* as an index.