Motion estimation and inter-mode prediction
An inter-mode for encoding a video macroblock is selected based on a comparison of at least two rate-distortion values associated with inter-modes. The number of potential inter-modes for encoding the video macroblock is initially reduced based on the rate-distortion calculation of the SKIP mode between the current macroblock and the collocated macroblock (corresponding to a 0,0 motion vector). Motion estimation is performed on the remaining inter-modes to identify reference blocks and motion vectors. The number of calculations performed in identifying the reference blocks and motion vectors is potentially reduced because associations between inter-modes are recognized and leveraged.
1. A non-transitory medium encoded with instructions for directing one or more processors to perform a method of selecting one of a plurality of inter-modes for encoding a macroblock, the method comprising:
calculating a rate-distortion value representative of the amount of distortion within the macroblock;
reducing the number of potential inter-modes that are to be analyzed for the macroblock based on the rate distortion value, comprising selecting a first set of inter-modes for analysis if the rate-distortion value is below a first threshold, and selecting a second set of inter-modes for analysis if the rate-distortion value is above the first threshold and below a second threshold, the first set of inter-modes being selected from the group consisting of a skip mode, a 16×16 mode, and an 8×8 mode;
identifying a first reference block and first motion vector associated with a first inter-mode; and
using the first reference block and first motion vector in performing motion estimation for a second inter-mode.
2. The method of claim 1 , wherein the rate-distortion value is a rate-distortion cost of the skip mode for the macroblock.
3. The method of claim 1 , wherein the potential inter-modes are defined by the H.264 standard.
4. The method of claim 1 , wherein the first reference block and first motion vector are identified using a diamond search in a reference frame.
5. The method of claim 1 , wherein the first reference block is used to create a search area within a reference frame to identify a second reference block.
6. The method of claim 5 , wherein the first motion vector is used to identify a starting position within the search area.
7. An encoder for selecting one of a plurality of inter-modes for encoding a macroblock, the encoder comprising:
a motion estimation module configured to receive the macroblock and to calculate a rate-distortion value representative of the amount of distortion with the macroblock; and
a mode selector module coupled to communicate with the motion estimation module and configured to reduce the number of potential inter-modes that are to be analyzed for the macroblock based on the rate distortion value, the mode selector module being further configured to select a first set of inter-modes for analysis if the rate-distortion value is below a first threshold, and select a second set of inter-modes for analysis if the rate-distortion value is above the first threshold and below a second threshold, the first set of inter-modes being selected from the group consisting of a skip mode, a 16×16 mode, and an 8×8 mode;
wherein the motion estimation module is further configured to identify a first reference block and first motion vector associated with a first inter-mode, and to use the first reference block and first motion vector in performing motion estimation for a second inter-mode.
8. The encoder of claim 7 , wherein the rate-distortion value is a rate-distortion cost of the skip mode for the macroblock.
9. The encoder of claim 7 , wherein the potential inter-modes are defined by the H.264 standard.
10. The encoder of claim 7 , wherein the first reference block and first motion vector are identified using a diamond search in a reference frame.
11. The encoder of claim 7 , wherein the first reference block is used to create a search area within a reference frame to identify a second reference block.
12. The encoder of claim 11 , wherein the first motion vector is used to identify a starting position within the search area.