System and method for media stream indexing and synchronization
An indexing system and method for allowing a viewer to control the mode of delivery of program material. By mapping from time to data position, data delivery can begin at any selected time in the program material. The indexing method also provides for controlling data delivery to begin at the beginning of a frame of data. A synchronizing method is provided to minimize a time offset between audio and video data, particularly in environments using groups of pictures.
1. A method for locating program material at a specified time T, comprising:
converting the specified time T to a time T rel , relative to media data representing the program material;
determining an index number from said time T rel using an index duration;
converting said index number to a data position, thereby locating media data representing the program material at the specified time T; and
converting a specified-segment relative time T seg to a specified-atom relative time T atom by adding a specified segment's offset to T seg , and computing an index number from T atom using an index duration.
2. The method of claim 1 , wherein said index duration is a duration of one frame of media data.
3. The method of claim 1 , further comprising: rounding said index number to locate an index boundary.
4. The method of claim 3 , wherein said index boundary is a beginning of a frame of media data.
5. The method of claim 3 , wherein said index boundary is a beginning of a group of pictures of media data.
6. A method as in claim 1 , wherein the method for locating program material comprises locating the program material so that delivery of the program material to a viewer via media delivery on demand begins at the specified time T in the program material.
7. A method as in claim 1 , further comprising accessing a group having one or more series, each series having one or more segments that references a corresponding atom containing the media data representing the program material.
8. A method as in claim 7 , further comprising determining in which specified segment of which specified atom of media data the specified time T occurs.
9. A method as in claim 8 , further comprising converting the specified time T to the specified-segment relative time T seg by calculating an elapsed time into the specified segment at which the specified time occurs.
10. A method as in claim 1 , wherein an index file is used to correlate index number with a corresponding data position.
11. A method as in claim 10 , wherein the corresponding data positions are the beginning of a frame of media data, or the beginning of a group of media items of media data.
12. A method as in claim 11 , wherein the media items include pictures.
13. A computer program product stored on a computer readable medium for use with a computer system and a content on demand media delivery system including computer readable program code for enabling a computer system to carry out the locating of program material so that delivery of the program material to a viewer via media delivery on demand begins at the specified time T in the program material; the computer program product including instructions for:
converting the specified time T to a time T rel relative to media data representing the program material;
determining an index number from said time T rel using an index duration;
converting said index number to a data position, thereby locating media data representing the program material at the specified time T; and
converting a specified-segment relative time T seg to a specified-atom relative time T atom by adding a specified segment's offset to T seg , and computing an index number from T atom using an index duration.