Method and system for video encoding using a variable number of B frames

A video coding method, comprising, from a sequence of video data:

• calculating, via a video coding system, motion vectors for a first picture temporally closest to a reference picture, wherein the reference picture and the first picture temporally closest to the reference picture are part of the sequence;
• determining, via the video coding system, a motion speed of the first picture based on the computed motion vectors for the first picture;
• for a plurality of pictures in the sequence following the first picture, until a termination condition is met:
• calculating, via the video coding system, motion vectors for a respective picture in the plurality of pictures,
• determining, via the video coding system, a motion speed for the respective picture based on the calculated motion vectors for the respective picture,
• comparing, via the video coding system, the motion speed of the respective picture with the motion speed of the first picture, and
• coding, via the video coding system, the respective picture as a B picture if the motion speeds are consistent with each other;
• and
• when the termination condition is met, coding, via the video coding system, the respective picture as a P picture.

Apparatus, comprising:

• a memory to store pictures of a video sequence,
• a video coder coupled to the memory, to code each stored picture as one of an I picture, a P picture and a B picture,
• a motion vector generator coupled to the memory to generate motion vectors for a first plurality of stored pictures, wherein the first plurality consists of a first picture temporally closest to a reference picture, temporally followed immediately by a second plurality of pictures,
• a colinearity detector having an input coupled to the output of the motion vector generator, the colinearity detector determining a motion speed for each of the first plurality of pictures based on the motion vectors of each respective picture and comparing the motion speeds of the second plurality of pictures to the motion speed of the first picture, and
• a picture type decision unit to assign pictures having generally consistent motion speeds for B picture coding and to assign a picture that does not exhibit consistent motion speed for coding as a P picture.

A video coding assignment method, comprising, for each of a first plurality of pictures in a sequence of video data following a reference picture in the sequence, wherein the first plurality of pictures consists of a first picture temporally closest to the reference picture, temporally followed immediately by a second plurality of pictures:

• adding, via a video coding system, the first picture to a group of frames,
• calculating, via the video coding system, motion vectors for the first picture;
• determining, via the video coding system, a motion speed of the first picture based on the computed motion vectors for the first picture;
• iteratively, for the second plurality of pictures subsequent to the first picture in the sequence and in display order:
• adding, via the video coding system, the subsequent picture to the group of frames,
• calculating, via the video coding system, motion vectors for each subsequent picture;
• determining, via the video coding system, a motion speed of the subsequent picture-based on the calculated motion vectors for the subsequent picture, if the motion speed of the subsequent picture is consistent with the motion speed of the first picture, performing a next iteration, and if not, coding, via the video coding system, the last picture of the group of frames as a P picture and coding all other pictures in the group of frames as a B picture.

A method of assigning frame types for coding of pictures in a video sequence, comprising:

• computing, via a video coding system, motion vectors for each pixelblock of each of a first plurality of pictures in the video sequence following a reference picture in the video sequence in temporal order, wherein the first plurality of pictures consists of a first picture temporally closest to the reference picture, temporally followed immediately by a second plurality of pictures,
• determining, via the video coding system, a motion speed for each pixelblock in the first picture based on the computed motion vectors for the first picture,
• for each picture in the second plurality of pictures, until a termination condition is met:
• determining, via the video coding system, a motion speed for each pixelblock in the respective picture based on the computed motion vectors for the respective picture,
• calculating, via the video coding system, a motion speed error for the respective picture by comparing the motion speed of each pixelblock in the respective picture with the motion speed of each pixelblock in the first picture, and
• coding, via the video coding system, the respective picture as a B picture if the motion speed error is less than a predetermined threshold,
• coding, via the video coding system, the respective picture as a P picture if the motion speed error is more than a predetermined threshold, wherein the termination condition is met when the respective picture is coded as a P picture.