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This disclosure describes scalable video coding techniques. In particular, the techniques may be used to encode refinements of a video block for enhancement layer bit streams in a single coding pass, thereby reducing coding complexity, coding delay and memory requirements. In some instances, the tec

This disclosure describes scalable video coding techniques. In particular, the techniques may be used to encode refinements of a video block for enhancement layer bit streams in a single coding pass, thereby reducing coding complexity, coding delay and memory requirements. In some instances, the techniques encode each nonzero coefficient of a coefficient vector of the enhancement layer without knowledge of any subsequent coefficients. Coding the enhancement layer in a single pass may eliminate the need to perform a first pass to analyze the coefficient vector and a second pass for coding the coefficient vector based on the analysis.

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1. A method of encoding video data using scalable video coding, the method comprising: encoding, by a video coding apparatus, a video block at a first quality as part of a base layer bit stream;encoding, by the video coding apparatus, as part of at least one enhancement layer bit stream, refinements

1. A method of encoding video data using scalable video coding, the method comprising: encoding, by a video coding apparatus, a video block at a first quality as part of a base layer bit stream;encoding, by the video coding apparatus, as part of at least one enhancement layer bit stream, refinements of the video block that when combined with the video block encoded at the first quality results in the video block having a second quality that is greater than the first quality, wherein the refinements of the video block are encoded without performing a first coding pass to gather statistics to use in video coding table selection,wherein the refinements are at least one of additional coefficients and refinements to existing coefficients, andwherein encoding the refinements comprises encoding, for each nonzero coefficient of the refinements of the video block, a symbol to indicate there is at least one remaining nonzero coefficient, a run length to indicate a number of zero valued coefficients preceding the nonzero coefficient, and a sign of the nonzero coefficient; andadjusting, with the video coding apparatus, magnitudes of the nonzero coefficients of the refinements of the video block to be equal to one. 2. The method of claim 1, wherein encoding the refinements of the video block comprises encoding each nonzero coefficient of the refinements without analyzing any subsequent coefficients. 3. The method of claim 1, further comprising encoding a symbol to indicate that there are no remaining nonzero coefficients in the refinements of the video block after encoding a last nonzero coefficient. 4. The method of claim 1, wherein adjusting the magnitude of each of the nonzero coefficients of the refinements of the video block to be equal to one comprises encoding the nonzero coefficients without encoding magnitudes of the coefficients. 5. The method of claim 1, wherein encoding the refinements of the video block as part of the enhancement layer bit stream comprises encoding the refinements of the video block such that coefficients of the refinements of the video block are decodable without accessing coefficient information of the video block encoded at the first quality as part of the base layer bit stream. 6. The method of claim 1, further comprising encoding the refinements of the video block using only a single variable length coding (VLC) table. 7. The method of claim 1, wherein encoding the video block at the first quality as part of the base layer comprises encoding the video block at the first quality using a coding technique that analyzes a coefficient vector of the video block in one coding pass and encodes the coefficient vector in another coding pass based on the analysis. 8. The method of claim 7, wherein: encoding the video block at the first quality comprises encoding the video block at the first quality using a context adaptive variable length coding (CAVLC) process in accordance with the ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard; andencoding the refinements of the video block comprises encoding the refinements of the video block using one of the VLC tables defined in the CAVLC process. 9. The method of claim 1, wherein the first and second qualities comprise one of a first and second signal-to-noise ratio (SNR) and a first and second spatial resolution. 10. A device for encoding video data using scalable video coding, the device comprising: a memory device storing a software program or executable instruction; andat least one encoder comprising one or more processors in communication with the memory device to execute the software program or executable instruction, the one or more processors configured to:encode a video block at a first quality as part of a base layer bit stream;encode, as part of at least one enhancement layer bit stream, refinements of the video block that when combined with the video block encoded at the first quality results in the video block having a second quality that is greater than the first quality, wherein the refinements of the video block are encoded without performing a first coding pass to gather statistics to use in video coding table selection, and wherein the refinements are at least one of additional coefficients and refinements to existing coefficients;encode, for each nonzero coefficient of the refinements of the video block, a symbol to indicate there is at least one remaining nonzero coefficient, a run length to indicate a number of zero valued coefficients preceding the nonzero coefficient, and a sign of the nonzero coefficient; andadjust magnitudes of the nonzero coefficients of the refinements of the video block to be equal to one. 11. The device of claim 10, wherein the at least one encoder encodes each nonzero coefficient of the refinements without analyzing any subsequent coefficients. 12. The device of claim 10, wherein the at least one encoder encodes a symbol to indicate that there are no remaining nonzero coefficients in the refinements of the video block after encoding a last nonzero coefficient. 13. The device of claim 10, wherein the at least one encoder encodes the nonzero coefficients without encoding magnitudes of the coefficients. 14. The device of claim 10, wherein the at least one encoder encodes the refinements of the video block such that coefficients of the refinements of the video block are decodable without accessing coefficient information of the video block encoded at the first quality as part of the base layer bit stream. 15. The device of claim 10, wherein the at least one encoder encodes the refinements of the video block using only a single variable length coding (VLC) table. 16. The device of claim 10, wherein the at least one encoder encodes the video block at the first quality using a coding technique that analyzes a coefficient vector of the video block in one coding pass and encodes the coefficient vector in another coding pass based on the analysis. 17. The device of claim 16, wherein the at least one encoder: encodes the video block at the first quality comprises encoding the video block at the first quality using a context adaptive variable length coding (CAVLC) process in accordance with the ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard; andencodes the refinements of the video block comprises encoding the refinements of the video block using one of the VLC tables defined in the CAVLC process. 18. The device of claim 10, wherein the first and second qualities comprise one of a first and second signal-to-noise ratio (SNR) and a first and second spatial resolution. 19. The device of claim 10, wherein the at least one encoder comprises: a base layer encoder that encodes the video block at the first quality as part of a base layer bit stream, andan enhancement layer encoder that encodes, as part of the at least one enhancement layer bit stream, refinements of the video block that when combined with the video block encoded at the first quality results in the video block having the second quality that is greater than the first quality. 20. The device of claim 10, wherein the device comprises a wireless communication device. 21. The device of claim 10, wherein the device comprises an integrated circuit device. 22. A non-transitory computer-readable medium comprising instructions to cause one or more processors to: encode a video block at a first quality as part of a base layer bit stream; andencode, as part of at least one enhancement layer bit stream, refinements of the video block that when combined with the video block encoded at the first quality results in the video block having a second quality that is greater than the first quality, wherein the refinements of the video block are encoded without performing a first coding pass to gather statistics to use in video coding table selection,wherein the refinements are at least one of additional coefficients and refinements to existing coefficients, andwherein the instructions that cause the one or more processors to encode the refinements comprise instructions that cause the one or more processors to encode, for each nonzero coefficient of the refinements of the video block, a symbol to indicate there is at least one remaining nonzero coefficient, a run length to indicate a number of zero valued coefficients preceding the nonzero coefficient, and a sign of the nonzero coefficient; andadjust magnitudes of the nonzero coefficients of the refinements of the video block to be equal to one. 23. The computer-readable medium of claim 22, wherein the instructions cause one or more processors to encode each nonzero coefficient of the refinements without analyzing any subsequent coefficients. 24. The computer-readable medium of claim 22, wherein the instructions cause one or more processors to encode a symbol to indicate that there are no remaining nonzero coefficients in the refinements of the video block after encoding a last nonzero coefficient. 25. The computer-readable medium of claim 22, wherein the instructions cause one or more processors to encode the nonzero coefficients without encoding magnitudes of the coefficients. 26. The computer-readable medium of claim 22, wherein the instructions cause one or more processors to encode the refinements of the video block such that coefficients of the refinements of the video block are decodable without accessing coefficient information of the video block encoded at the first quality as part of the base layer bit stream. 27. The computer-readable medium of claim 22, wherein the instructions cause one or more processors to encode the refinements of the video block using only a single variable length coding (VLC) table. 28. The computer-readable medium of claim 22, wherein the instructions cause one or more processors to encode the video block at the first quality using a coding technique that analyzes a coefficient vector of the video block in one coding pass and encodes the coefficient vector in another coding pass based on the analysis. 29. The computer-readable medium of claim 28, wherein the instructions cause one or more processors to: encode the video block at the first quality comprises encoding the video block at the first quality using a context adaptive variable length coding (CAVLC) process in accordance with the ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard; andencode the refinements of the video block comprises encoding the refinements of the video block using one of the VLC tables defined in the CAVLC process. 30. The computer-readable medium of claim 22, wherein the first and second qualities comprise one of a first and second signal-to-noise ratio (SNR) and a first and second spatial resolution. 31. A device for encoding video data using scalable video coding, the device comprising: a processor; anda memory storing computer executable instructions that when executed by the processor, cause the processor to implement:first means for encoding a video block at a first quality as part of a base layer bit stream; andsecond means for encoding, as part of at least one enhancement layer bit stream, refinements of the video block that when combined with the video block encoded at the first quality results in the video block having a second quality that is greater than the first quality, wherein the refinements of the video block are encoded without performing a first coding pass to gather statistics to use in video coding table selection, wherein the refinements are at least one of additional coefficients and refinements to existing coefficients,wherein the second means for encoding means encodes, for each nonzero coefficient of the refinements of the video block, a symbol to indicate there is at least one remaining nonzero coefficient, a run length to indicate the number of zero valued coefficients preceding the nonzero coefficient, and a sign of the nonzero coefficient, andwherein the second means for encoding means adjusts magnitudes of the nonzero coefficients of the refinements of the video block to be equal to one. 32. The device of claim 31, wherein the second means for encoding encodes each nonzero coefficient of the refinements without analyzing any subsequent coefficients. 33. The device of claim 32, wherein the second means for encoding encodes a symbol to indicate that there are no remaining nonzero coefficients in the refinements of the video block after encoding a last nonzero coefficient. 34. The device of claim 31, wherein the second means for encoding encodes the nonzero coefficients without encoding magnitudes of the coefficients. 35. The device of claim 31, wherein the second means for encoding encodes the refinements of the video block such that coefficients of the refinements of the video block are decodable without accessing coefficient information of the video block encoded at the first quality as part of the base layer bit stream. 36. The device of claim 31, wherein the second means for encoding encodes the refinements of the video block using only a single variable length coding (VLC) table. 37. The device of claim 31, wherein the first means for encoding the video block at the first quality as part of the base layer comprises means for encoding the video block at the first quality using a coding technique that analyzes a coefficient vector of the video block in one coding pass and encodes the coefficient vector in another coding pass based on the analysis. 38. The device of claim 37, wherein the first means for encoding: encodes the video block at the first quality comprises encoding the video block at the first quality using a context adaptive variable length coding (CAVLC) process in accordance with the ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard; andencodes the refinements of the video block comprises encoding the refinements of the video block using one of the VLC tables defined in the CAVLC process. 39. The device of claim 31, wherein the first and second qualities comprise one of a first and second signal-to-noise ratio (SNR) and a first and second spatial resolution. 40. A method for decoding video data using scalable video coding, the method comprising: decoding, by a video coding apparatus, a base layer bit stream to obtain a video block at a first quality;decoding, by the video coding apparatus, an enhancement layer bit stream to obtain refinements of the video block that, when combined with the video block decoded at the first quality, result in the video block having a second quality,wherein the refinements are at least one of additional coefficients and refinements to existing coefficients, andwherein decoding the enhancement layer includes decoding, for each nonzero coefficient of the refinements of the video block, a symbol indicating there is at least one remaining nonzero coefficient, a run length indicating a number of zero valued coefficients preceding the nonzero coefficient and a sign of the nonzero coefficient; andsetting, with the video coding apparatus, a magnitude of each nonzero coefficient equal to one. 41. The method of claim 40, further comprising decoding a symbol following a last nonzero coefficient that indicates that there are no remaining nonzero coefficients in the refinements of the video block. 42. The method of claim 41, further comprising generating a vector of coefficients for the refinements of the video block using the decoded run of each coefficient, the sign of each coefficient and the symbol indicating that there are no remaining nonzero coefficients. 43. The method of claim 40, wherein decoding the refinements of the video block comprises decoding the refinements of the video block without accessing coefficient information of the video block encoded at the first quality. 44. The method of claim 40, further comprising decoding the refinements of the video block using only a single variable length coding (VLC) table. 45. The method of claim 44, wherein the single VLC table comprises one of the VLC tables specified in CAVLC as defined in ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard. 46. A device for decoding video data using scalable video coding, the device comprising: a memory device storing a software program or executable instruction; andat least one decoder comprising one or more processors in communication with the memory device to execute the software program or executable instruction, the one or more processors configured to:decode a base layer bit stream to obtain a video block at a first quality;decode an enhancement layer bit stream to obtain refinements of the video block that, when combined with the video block decoded at the first quality, result in the video block having a second quality,wherein the refinements are at least one of additional coefficients and refinements to existing coefficients, andwherein the at least one decoder decodes for each nonzero coefficient of the refinements of the video block, a symbol indicating there is at least one remaining nonzero coefficient, a run length indicating a number of zero valued coefficients preceding the nonzero coefficient and a sign of the nonzero coefficient; andset a magnitude of each nonzero coefficient equal to one. 47. The device of claim 46, wherein the at least one decoder decodes a symbol following a last nonzero coefficient that indicates that there are no remaining nonzero coefficients in the refinements of the video block. 48. The device of claim 47, wherein the at least one decoder generates a vector of coefficients for the refinements of the video block using the decoded run of each coefficient, the sign of each coefficient and the symbol indicating that there are no remaining nonzero coefficients. 49. The device of claim 46, wherein the at least one decoder decodes the refinements of the video block without accessing coefficient information of the video block encoded at the first quality. 50. The device of claim 46, wherein the at least one decoder decodes the refinements of the video block using only a single variable length coding (VLC) table. 51. The device of claim 50, wherein the single VLC table comprises one of the VLC tables specified in CAVLC as defined in ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard. 52. The device of claim 46, wherein the at least one decoder comprises: a base layer decoder that decodes the base layer bit stream to obtain the video block at the first quality; andan enhancement layer decoder that decodes the enhancement layer bit stream to obtain the refinements of the video block. 53. The device of claim 46, wherein the device comprises a wireless communication device. 54. The device of claim 46, wherein the device comprises an integrated circuit device. 55. A non-transitory computer-readable medium comprising instructions to cause one or more processors to: decode a base layer bit stream to obtain a video block at a first quality;decode an enhancement layer bit stream to obtain refinements of the video block that, when combined with the video block decoded at the first quality, result in the video block having a second quality,wherein the refinements are at least one of additional coefficients and refinements to existing coefficients, andwherein the instructions cause the one or more processors to decode for each nonzero coefficient of the refinements of the video block, a symbol indicating there is at least one remaining nonzero coefficient, a run length indicating a number of zero valued coefficients preceding the nonzero coefficient and a sign of the nonzero coefficient; andset a magnitude of each nonzero coefficient equal to one. 56. The computer-readable medium of claim 55, wherein the instructions cause one or more processors to decode a symbol following a last nonzero coefficient that indicates that there are no remaining nonzero coefficients in the refinements of the video block. 57. The computer-readable medium of claim 56, wherein the instructions cause one or more processors to generate a vector of coefficients for the refinements of the video block using the decoded run of each coefficient, the sign of each coefficient and the symbol indicating that there are no remaining nonzero coefficients. 58. The computer-readable medium of claim 55, wherein the instructions cause one or more processors to decode the refinements of the video block without accessing coefficient information of the video block encoded at the first quality. 59. The computer-readable medium of claim 55, wherein the instructions cause one or more processors to decode the refinements of the video block using only a single variable length coding (VLC) table. 60. The computer-readable medium of claim 59, wherein the single VLC table comprises one of the VLC tables specified in CAVLC as defined in ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard. 61. A device for decoding video data using scalable video coding, the device comprising: a processor; anda memory storing computer executable instructions that when executed by the processor, cause the processor to implement:first means for decoding a base layer bit stream to obtain a video block at a first quality; andsecond means for decoding an enhancement layer bit stream to obtain refinements of the video block that, when combined with the video block decoded at the first quality, result in the video block having a second quality,wherein the refinements are at least one of additional coefficients and refinements to existing coefficients, andwherein the second means for decoding means decodes, for each nonzero coefficient of the refinements of the video block, a symbol indicating there is at least one remaining nonzero coefficient, a run length indicating a number of zero valued coefficients preceding the nonzero coefficient and a sign of the nonzero coefficient; andmeans for setting a magnitude of each nonzero coefficient equal to one. 62. The device of claim 61, wherein the second means for decoding decodes a symbol following a last nonzero coefficient that indicates that there are no remaining nonzero coefficients in the refinements of the video block. 63. The device of claim 62, further comprising means for generating a vector of coefficients for the refinements of the video block using the decoded run of each coefficient, the sign of each coefficient and the symbol indicating that there are no remaining nonzero coefficients. 64. The device of claim 61, wherein the second means for decoding decodes the refinements of the video block without accessing coefficient information of the video block encoded at the first quality. 65. The device of claim 61, wherein the second means for decoding decodes the refinements of the video block using only a single variable length coding (VLC) table. 66. The device of claim 65, wherein the single VLC table comprises one of the VLC tables specified in CAVLC as defined in ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC) standard.