Entropy encoding and decoding using direct level and run-length/level context-adaptive arithmetic coding/decoding modes

摘要

An encoder performs context-adaptive arithmetic encoding of transform coefficient data. For example, an encoder switches between coding of direct levels of quantized transform coefficient data and run-level coding of run lengths and levels of quantized transform coefficient data. The encoder can determine when to switch between coding modes based on a pre-determined switch point or by counting consecutive coefficients having a predominant value (e.g., zero). A decoder performs corresponding context-adaptive arithmetic decoding.

主权项

1. A computing device that implements an encoder, the computing device comprising:
one or more processors; memory; and one or more storage media storing instructions for causing the computing device to perform a method of encoding audio or video data, the method comprising: performing a frequency transform on a block of plural samples to produce plural transform coefficients;
quantizing the plural transform coefficients; andentropy coding the plural quantized transform coefficients, wherein the entropy coding includes:
encoding one or more of the plural quantized transform coefficients using a direct level encoding mode, including performing first context-adaptive arithmetic coding of a level value of a given coefficient of the plural quantized transform coefficients, wherein the first context-adaptive arithmetic coding uses a first set of plural contexts, and wherein the first context-adaptive arithmetic coding includes selecting one of the first set of plural contexts based at least in part on level values of two previously encoded quantized transform coefficients;switching to a run-level encoding mode for remaining coefficients of the plural quantized transform coefficients;encoding the remaining quantized transform coefficients using the run-level encoding mode, including:performing second context-adaptive arithmetic coding of a non-zero level value of one of the remaining quantized transform coefficients, wherein the second context-adaptive arithmetic coding uses a second set of plural contexts different than the first set of plural contexts, and wherein the second context-adaptive arithmetic coding includes selecting one of the second set of plural contexts based at least in part on a level value of a previously encoded quantized transform coefficient; andperforming third context-adaptive arithmetic coding of a run value, the run value indicating a count of consecutive zero-value remaining quantized transform coefficients adjacent the remaining quantized transform coefficient with the non-zero level value, wherein the third context-adaptive arithmetic coding uses a third set of plural contexts different than the first set of plural contexts and different than the second set of plural contexts.