DCT/Q/IQ/IDCT bypass algorithm in MPEG to AVC/H.264 transcoding

摘要

In one embodiment, a first DCT block of coefficients is received from a transcoding process. The DCT block is of a first size, such as an 8×8 size, and in a first coding standard, such as MPEG-2. A distribution of zero and non-zero coefficients is then determined from the first DCT block. For example, areas where non-zero coefficients are found may be determined. This may simplify a corresponding sum of absolute difference (SAD) calculation. The SAD is then calculated for a second DCT block of a second size, such as a 4×4 size block, in a second coding standard, such as AVC. The SAD is determined from the coefficients in the first DCT block. Accordingly, the SAD is determined without performing an inverse DCT on the 8×8 block and then computing the SAD for a 4×4 block. It is then determined if a bypass of a DCT operation for the 4×4 block can be performed based on the SAD computed. For example, the SAD is compared to a threshold to determine if a bypass can be performed. In one example, if the coefficients for each 4×4 block are determined that they may be quantized to zero, then the DCT operation may be bypassed. Also, quantization, inverse quantization, and inverse DCT steps may also be bypassed.