Method and apparatus for multiple description video coding
A method and apparatus for utilizing temporal prediction and motion compensated prediction to accomplish multiple description video coding is disclosed. An encoder receives a sequence of video frames and divides each frame into non-overlapping macroblocks. Each macroblock is then encoded using either an intraframe mode (I-mode) or a prediction mode (P-mode) technique. Both the I-mode and the P-mode encoding techniques produce an output for each of n channels used to transmit the encoded video data.
1. An encoder comprising:
a first module responsive to a video frame, the first module configured to divide the video frame into macroblocks;
a mode selection element configured to select each of the macroblocks for intra-frame coding mode (I-mode) encoding or for predictive coding mode (P-mode) encoding;
an I-mode module configured to encode a first macroblock that is selected for I-mode encoding by coding color values of the first macroblock into an I-mode first description of a multiple description coding scheme and into an I-mode second description of the multiple description coding scheme; and
a P-mode module configured to encode a second macroblock that is selected for P-mode encoding by coding both a motion vector and an error into a first P-mode description and into a second P-mode description by predicting the second macroblock based on a previously encoded frame.
2. The encoder of claim 1 , wherein the error corresponds to a difference between the second macroblock and another macroblock from a previous frame that is used to predict the second macroblock.
3. The encoder of claim 2 , wherein the motion vector is descriptive of displacement between the second macroblock and a best matching macroblock.
4. The encoder of claim 3 , wherein both the error and the motion vector are coded into multiple descriptions.
5. The encoder of claim 1 , wherein the mode selection element applies one macroblock to the I-mode module for every x macroblocks that are routed to the P-mode module, where x is a number between 10 and 15.
6. The encoder of claim 1 , further comprising a rate control unit, wherein the rate control unit is configured to influence whether the mode selection element applies each of the macroblocks to the I-mode module or to the P-mode module.
7. A method for encoding video frames comprising:
dividing a video frame into macroblocks;
selecting each of the macroblocks for I-mode encoding or for P-mode encoding;
encoding a first macroblock that is selected for I-mode encoding by coding color values of the first macroblock into an I-mode first description of a multiple description coding scheme and an I-mode second description of the multiple description coding scheme; and
encoding a second macroblock that is selected for P-mode encoding by coding both a motion vector and an error into a P-mode first description and into a P-mode second description.
8. The method of claim 7 , wherein the motion vector represents a displacement between the second macroblock and a best matching macroblock.
9. The method of claim 7 , wherein a first set of descriptions comprises the I-mode first description and the I-mode second description, and wherein, when one description of the first set of descriptions is not received, the video frame can be reconstructed by using another description of the first set of descriptions.
10. The method of claim 9 , wherein a second set of descriptions comprises the P-mode first description and the P-mode second description, and wherein, when one description of the second set of description is not received, the video frame can be reconstructed by using another description of the second set of descriptions.
11. The method of claim 7 , wherein the error corresponds to a difference between the second macroblock and a previously encoded frame.
12. The method of claim 7 , wherein both the error and the motion vector are coded into multiple descriptions.
13. The method of claim 7 , wherein the I-mode encoding is applied to one macroblock for every x macroblocks, where x is a number between 10 and 15.
14. The method of claim 7 , wherein a determination as to whether to apply the I-mode encoding or the P-mode encoding to a particular macroblock is responsive to a rate control unit.
15. The method of claim 7 , wherein a determination as to whether to apply the I-mode encoding or the P-mode encoding to a particular macroblock is responsive to a redundancy allocation unit.