Hypothetical reference decoder

1. A method comprising:

(a) defining a first set of at least one value characteristic of a transmission bit rate for a first segment of a video having an associated first segment presentation start time and an associated first segment presentation end time;

(b) defining a second set of at least one value characteristic of a buffer size for said first segment;

(c) defining a third set of at least one value characteristic of an initial decoder buffer fullness for said first segment;

(d) wherein each value within said first set, said second set, and said third set, respectively, is defined so that data received by a decoder for constructing a plurality of video frames of said first segment is free from an underflow state in a buffer of said decoder when said constructing begins at said first segment presentation start time;

(e) defining a fourth set of at least one value characteristic of said transmission bit rate for a second segment of said video having an associated second segment presentation start time and an associated second segment presentation end time, said second segment presentation start time being later than first segment presentation start time and said second segment presentation end time being the same as, or earlier, than said first segment presentation end time;

(f) defining a fifth set of at least one value characteristic of said buffer size for said second segment;

(g) defining a sixth set of at least one value characteristic of said initial decoder buffer fullness for said second segment;

(h) wherein each value within said fourth set, said fifth set, and said sixth set, respectively, is defined so that data received by said decoder for constructing a plurality of video frames of said second segment is free from an underflow state in said buffer of said decoder when said constructing begins at said second segment presentation start time; and

(i) allowing a user to begin presentation at a user-selected one of said first segment presentation start time, and said second segment presentation start time associated with said second segment.

2. The method of claim 1 wherein said first set, second set, and third set of respective values together define at least one leaky bucket model for a buffer of a hypothetical reference decoder.

3. The method of claim 1 wherein said second segment presentation start time corresponds to a local maximum buffer fullness state of a said leaky bucket model constructed using values defined for said first segment of said video.

4. The method of claim 2 wherein said at least one leaky bucket model uses a fixed transmission bit rate.

5. The method of claim 2 wherein said at least one leaky bucket model uses a variable transmission bit rate.

6. The method of claim 1 including defining further respective sets of at least one value characteristic of a transmission bit rate, a buffer size, and an initial buffer fullness, respectively, each respective further set associated with another respective segment of said video having a presentation start time later than said second segment presentation start time, and a presentation end time the same as, or earlier, than said first segment presentation end time.

7. The method of claim 1 wherein steps (a) through (h) are performed at an encoder having a buffer fullness state complementary to said buffer of said decoder.

8. The method of claim 2 wherein said sixth set of at least one value is at least 90% of the buffer size of said at least one leaky bucket model.

9. The method of claim 1 wherein said fourth set of at least one value equals said first set of at least one value.

10. The method of claim 1 wherein said fifth set of at least one value equals said second set of at least one value.

11. The method of claim 1 wherein said sixth set of at least one value equals said third set of at least one value.

12. A method of encoding video, comprising:

defining a first set of values R i (where i=1,2, . . . N) characteristic of a transmission bit rate for a video segment;

defining a second set of values B i (where i=1,2, . . . N) characteristic of a buffer size for the video segment;

defining a third set of values D i1 (where i=1,2, . . . N) characteristic of a delay until the video segment is presented;

wherein the first set of values, the second set of values, and the third set of values are defined for the video segment as a whole;

selecting, for a first portion of the video segment, one of the first set of values R i , one of the second set of values B i , and one of the third set of values D i1 such that the first portion of the video segment is free from an underflow condition and an overflow condition by using the selected values R i , B i and D i1 as a transmission bit rate, a buffer size and a delay until the first portion of the video segment is presented respectively;

defining, for a second portion of the video segment, a fourth set of values D ij (where i=1,2, . . . N) characteristic of a delay until the second portion of the video segment is presented,

wherein the second portion of the video segment is a portion after a prescribed position in the first portion of the video segment; and

selecting, for the second portion of the video segment, one of the fourth set of values D ij , wherein the selecting are such that the second portion of the video segment is free from an underflow condition and an overflow condition by using the unchanged values R i , B i and the selected value D ij as the transmission bit rate, the buffer size and a delay of the fourth set of values until the second portion of the video segment is presented respectively.