System and method for seamless switching of compressed audio streams

1. A method of preparing a plurality of digital audio fragments to allow switching between at least one source audio fragment and at least one target audio fragment said method comprising:

aligning an end of said at least one source audio fragment, the source audio fragment having a length which is not an exact multiple of a frame size of an encoding system, with a beginning of said at least one target audio fragment, for all possible valid combinations of said at least one source audio fragment and said at least one target audio fragment;

altering said at least one source audio fragment and at least one target audio fragment such that the at least one source audio fragment is made to be a length that is an exact multiple of the frame size; and

encoding the at least one source audio fragment and the at least one target audio fragment according to the encoding system.

2. The method of claim 1 , wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises:

moving a sequence of audio samples from at least one a digital audio fragment to at least one other digital audio fragment.

3. The method of claim 2 wherein said moved sequence of audio samples is a length which will result in said at least one source audio fragment to be a length that is an exact multiple of the frame size.

4. The method of claim 1 wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises:

moving a sequence of audio samples from said end of said at least one source audio fragment to said beginning of said at least one target audio fragment; wherein said sequence of audio samples is a length which will shorten said at least one source audio fragment to be a length that is an exact multiple of said frame size.

5. The method of claim 1 wherein altering the at least one source audio fragment and the at least one target audio fragment, further comprises:

moving a sequence of audio samples from said beginning of said at least one target audio fragment to said end of said at least one source audio fragment wherein said sequence of audio samples is a length which will lengthen said at least one source audio fragment to be a length that is an exact multiple of said frame size.

6. The method of claim 5 further including:

moving a second sequence of audio samples from said beginning of said at least one target audio fragment to said end of said at least one source audio fragment wherein said second sequence of audio samples is a length equal to said frame size.

7. The method of claim 1 , wherein encoding the at least one source audio fragment and the at least one target audio fragment according to the encoding system further comprises encoding a sequence of frames wherein a subsequent frame encoding is dependent upon an encoding of at least one preceding frame.

8. The method of claim 1 , wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises moving identical audio samples from the beginnings of said target audio fragments to the ends of said source audio fragments so that the resulting ends of said source audio fragments align at an exact multiple of said frame size, and the resulting last frames of each of said source audio fragments are identical.

9. The method of claim 1 , wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises moving identical audio samples from the beginnings of said target audio fragments to the ends of said source audio fragments so that the ends of said source audio fragments align at an exact multiple of said frame size, and wherein at least one audio sample is identical at the end of all of said source audio fragments, however the last full frame of audio samples are not identical for all said source audio fragments.

10. The method of claim 1 , wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises moving identical audio samples from the ends of said source audio fragments to the beginnings of said target audio fragments so that the resulting ends of said source audio fragments align at an exact multiple of said frame size, wherein at least one audio sample is identical at the beginnings of all of said target audio fragments, however the first full frame of audio samples is not identical for all said target audio fragments.

11. The method of claim 1 , wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises moving audio samples from the beginning of a first target audio fragment to the ends of said source audio fragments; and removing an identical number of audio samples from the beginnings of at least one remaining target audio fragment, so that the resulting ends of said source audio fragments align at an exact multiple of said frame size.

12. The method of claim 1 , wherein altering the at least one source audio fragment and the at least one target audio fragment further comprises moving audio samples from the end of a first source audio fragment to the beginnings of said target audio fragments; and removing an identical number of audio samples from the ends of at least one remaining source audio fragment, so that the resulting ends of said source audio fragments align at an exact multiple of said frame size.

13. The method of claim 1 , wherein at least one digital audio fragment has an end time that is later than the beginning time of any other digital audio fragments, and wherein an end of said at least one digital audio fragment is aligned at an exact multiple of said frame size by adding empty audio samples to the end of said at least one audio fragment.

14. The method of claim 7 , further including:

copying a last frame of a source audio fragment to the beginning of at least one target audio fragment;

encoding said at least one target audio fragment using said encoding system; and

removing data from the beginning of said compressed at least one target audio fragment, said data corresponding to a first frame of said at least one target audio fragment.

15. A system for preparing a plurality of digital audio fragments for transmission to allow a switching device to switch between at least one source audio fragment and at least one target audio fragment; said system comprising:

an audio aligner module, coupled to a source of said plurality of audio fragments, at least a plurality of which have lengths that are not an exact multiple of a frame size of an encoding system, configured to align beginnings and ends of said plurality of audio fragments to selected times based on an exact multiple of the frame size;

an audio encoding module, coupled to said audio aligner module, configured to encode said plurality of audio fragments as a sequence of frames, wherein each frame comprises a sequence of audio samples; and wherein a length of said frame is said frame size.

16. The system of claim 15 , wherein said plurality of audio fragments are transmitted using a transport mechanism selected from one of MPEG compliant, digital television, DVD broadcast, DVD storage, CD ROM, and the Internet.

17. The system of claim 15 , wherein said plurality of audio fragments are encoded using AC-3.

18. The system of claim 15 , wherein said plurality of audio fragments are encoded using MPEG Layer II.

19. A switching apparatus, to switch between a plurality of audio fragments, comprising:

a switching component configured to switch between at least one source audio fragment and at least one target audio fragment;

wherein said audio fragments are prepared by:

aligning an end of at least one source audio fragment, the source audio fragment having a length which is not an exact multiple of a frame size of an encoding system, with a beginning of at least one target audio fragment;

altering said at least one source audio fragment and at least one target audio fragment such that the at least one source audio fragment is made to be a length that is an exact multiple of the frame size; and

encoding the at least one source audio fragment and the at least one target audio fragment according to the encoding system.

20. The switching apparatus of claim 19 wherein said switching apparatus is configured to receive said plurality of audio fragments transmitted using a transport mechanism selected from one of MPEG compliant, digital television, DVD broadcast, DVD storage, CD ROM, and the Internet.

21. The switching apparatus of claim 19 wherein said switching apparatus is a receiver for MPEG encoded media streams.

22. The switching apparatus of claim 19 wherein said switching apparatus is selected from one of a set top box, a DVD player, a personal computer, a digital television set, a video server, and a video on demand server.

23. The switching apparatus of claim 19 , further comprising a memory module, said memory module configured to receive at least one target audio fragment at a time before switching to said at least one target audio fragment.