Systems and methods for decoding redundant motion vectors in compressed video bitstreams
The invention is related to methods and apparatus that decode robustly encoded video bitstreams. One embodiment of a decoder can advantageously reconstruct a predictive-coded video object plane (P-VOP) from a standard motion vector and the previous frame; from a redundant motion vector and a frame prior to the previous frame; or from both. Advantageously, this permits the decoder to display a frame based on a reconstructed VOP in the presence of unfavorable environmental conditions, such as interference, delays, and the like, which could otherwise corrupt a previous frame that is used as a reference by a standard decoder, such as a standard MPEG-4 decoder. One embodiment is advantageously backwards compatible with standard MPEG-4 compliant bitstreams and retrieves redundant motion vector information from user data video packets. One embodiment includes at least one extra frame buffer or memory, which stores a reference frame corresponding to a redundant motion vector.
1. A video decoder adapted to decode robustly encoded video information comprising: a demultiplexer adapted to parse data from the video bitstream; motion decoder configured to receive motion information from the demultiplexer, where the motion decoder is configured to be able to decode motion information for a standard motion vector, which is referenced to a previous frame, where the motion decoder is further configured to be able to decode motion information from a redundant motion vector, which is referenced to a frame prior to the previous frame; a texture decoder configured to receive texture information from the demultiplexer and decode a texture of the VOP; and a composition circuit adapted to combine multiple VOPs to generate a video frame.
2. The video decoder as defined in claim 1 , further comprising a shape decoder configured to receive shape information from the demultiplexer and decodes a shape of a video object plane (VOP) from the received data.
3. The video decoder as defined in claim 1 , wherein the motion decoder is configured to decode motion from the standard motion vector when the previous frame is available.
4. The video decoder as defined in claim 1 , wherein the motion decoder is configured to decode motion from the redundant motion vector when the previous frame is not available.
5. The video decoder as defined in claim 1 , wherein the motion decoder is configured to decode motion from both the standard motion vector and the redundant motion vector and is further configured to select between a VOP reconstructed from the standard motion vector and a VOP reconstructed from the redundant motion vector.
6. The video decoder as defined in claim 1 , wherein the motion decoder is configured to decode video bitstreams that are compliant with MPEG-4 syntax.
7. A video object plane (VOP) decoder in a video decoder that is adapted to decode a VOP in a first frame, comprising: a first memory configured to store a reconstructed VOP from a second frame, where the second frame is a frame immediately prior to the first frame; a second memory configured to store a reconstructed VOP from a third frame, where the third frame is a frame that is prior to the second frame; a first motion decoder configured to decode a standard motion vector from an encoded bitstream that is related to motion of the first reconstructed VOP in the first memory; a second motion decoder configured to decode a redundant motion vector from the encoded bitstream that is related to motion of the second reconstructed VOP in the second memory; and a motion compensator that is configured to reconstruct a VOP at least in part from information provided by at least one of the first motion decoder and the second motion decoder.
8. The VOP decoder as defined in claim 7 , wherein the third frame stored by the second memory is a frame that is immediately prior to the second frame.
9. The VOP decoder as defined in claim 7 , further comprising a selector module adapted to select between a VOP reconstructed at least in part from the standard motion vector and a VOP reconstructed at least in part from the redundant motion vector.
10. A video decoder configured to decode a video bitstream that includes redundant motion vectors for at least some predictive-coded video object planes (P-VOPs), the video decoder comprising: means for receiving the video bitstream; means for decoding video object planes (VOPS) of a first frame from the video bitstream; means for detecting that a first reference VOP from a second frame is not available, where the second frame is a reference frame for a standard motion vector for a P-VOP of the first frame; means for retrieving a redundant motion vector from the video bitstream, where the redundant motion vector uses a second reference VOP from a third frame earlier in time than the second frame as a reference; and means for reconstructing the P-VOP from the redundant motion vector and the second reference VOP.