METHOD AND APPARATUS FOR MANIPULATING BIT STREAMS
Trans-rating of successive macroblocks in a video stream occurs in accordance with the block type. For example, an (Inter) Intra-coded macroblock will generally get trans-rated using first algorithm partly decodes the macroblock and modifies coded residual coefficients by raising coefficient quantization. Intra-coded macroblocks generally get trans-rated using a second technique that operates first to decode the macroblock and then derive all the main decisions therefrom to re-encode the stream using the original decisions. Separately trans-rating Inter-coded and Intra-coded macroblocks in this manner reduces computational complexity, as compared to the use of a single trans-rating algorithm, while still maintaining good video quality.
1 . A method comprising the steps of:
analyzing a successive macroblock as well as previously trans-rated neighboring macroblocks blocks to establish a macroblock type; and
trans-rating the successive macroblock in accordance with the macroblock type.
2 . The method according to claim 1 wherein the analyzing step comprises the step of establishing the macroblock type as one of an intra-coded macroblock and an inter-coded macroblock.
3 . The method according to claim 2 wherein an inter-coded macroblock undergoes trans-rating in accordance with a first trans-rating technique.
4 . The method according to claim 2 wherein an intra-coded macroblock undergoes trans-rating in accordance with a second trans-rating technique.
5 . The method according to claim 3 wherein the first trans-rating technique partly decodes the macroblock and modifies coded residual coefficients by raising coefficient quantization.
6 . The method according to claim 4 wherein the second trans-rating technique decodes the macroblock and then derives decisions from the decoded macroblock for subsequent re-encoding.
7 . The method according to claim 4 wherein the intra-coded macroblock is trans-rated in accordance with the second technique so long as prediction information remains available.
8 . The method according to claim 7 wherein the intra-coded macroblock undergoes trans-rating in accordance with the first technique when no prediction information exists.
9 . Apparatus comprising:
a decoder for decoding a stream of macroblocks;
a macroblock analyzer for analyzing a successive macroblock as well as previously trans-rated neighboring macroblocks blocks to establish a macroblock type; and for trans-rating the successive macroblock in accordance with the macroblock type; and
an encoder for encoding the successive macroblock following trans-rating.
10 . The apparatus according to claim 1 wherein the macroblock analyzer establishes the macroblock type as one of an intra-coded macroblock and an inter-coded macroblock.
11 . The apparatus according to claim 10 wherein the macroblock analyzer trans-rates an inter-coded macroblock in accordance with a first trans-rating technique.
12 . The apparatus according to claim 10 wherein the macroblock analyzer trans-rates an intra-coded macroblock in accordance with a second trans-rating technique.
13 . The apparatus according to claim 11 wherein the first trans-rating technique partly decodes the macroblock and modifies coded residual coefficients by raising coefficient quantization.
14 . The apparatus according to claim 12 wherein the second trans-rating technique decodes the macroblock and then derives decisions from the decoded macroblock for subsequent re-encoding.
15 . The apparatus according to claim 12 wherein the macroblock analyzer trans-rates an intra-predictive macroblock in accordance with the second technique as long as prediction information remains available.
16 . The apparatus according to claim 15 wherein the macroblock analyzer trans-rates an intra-coded macroblock in accordance with the first technique when no prediction information exists.