A method for decoding video data, the method comprising: obtaining, by one or more processors of a video decoder and for a current block of a current picture of video data, values of motion vectors of an affine motion model of a neighboring block of video data; decoding, by the one or more processors and from an encoded video bitstream, a first syntax element included in a sequence parameter set, SPS, referred to by the current picture, wherein a first value of the syntax element indicates that motion compensation for pictures referring to the SPS can be performed using a four-parameter affine motion model defined by two motion vectors, and wherein a second value of the syntax element indicates that motion compensation for pictures referring to the SPS can be performed using either a four-parameter affine motion model defined by two motion vectors or a six-parameter affine motion model defined by three motion vectors; responsive to the first syntax element having the second value: decoding, by the one or more processors and from the encoded video bitstream, a second syntax element wherein a first value of the second syntax element indicates that motion compensation for the current block is to be performed using a four-parameter affine motion model defined by two motion vectors, and wherein a second value of the second syntax element indicates that motion compensation for the current block is to be performed using a six-parameter affine motion model defined by three motion vectors; and deriving, by the one or more processors and from the values of the motion vectors of the affine motion model of the neighboring block of video data, values of predictors for motion vectors of an affine motion model of the current block of video data indicated by the second syntax element; decoding, by the one or more processors and from the encoded video bitstream, a representation of differences between the values of the motion vectors of the affine motion model for the current block of video data and the values of the predictors; determining, by the one or more processors, each of the values of the motion vectors of the affine motion model for the current block of video data from the values of the predictors and the decoded differences; determining, based on the determined values of the motion vectors of the affine motion model for the current block of video data, a predictor block of video data; and reconstructing the current block of video data based on the predictor block of video data. obtaining, by one or more processors of a video decoder and for a current block of a current picture of video data, values of motion vectors of an affine motion model of a neighboring block of video data; decoding, by the one or more processors and from an encoded video bitstream, a first syntax element included in a sequence parameter set, SPS, referred to by the current picture, wherein a first value of the syntax element indicates that motion compensation for pictures referring to the SPS can be performed using a four-parameter affine motion model defined by two motion vectors, and wherein a second value of the syntax element indicates that motion compensation for pictures referring to the SPS can be performed using either a four-parameter affine motion model defined by two motion vectors or a six-parameter affine motion model defined by three motion vectors; responsive to the first syntax element having the second value: decoding, by the one or more processors and from the encoded video bitstream, a second syntax element wherein a first value of the second syntax element indicates that motion compensation for the current block is to be performed using a four-parameter affine motion model defined by two motion vectors, and wherein a second value of the second syntax element indicates that motion compensation for the current block is to be performed using a six-parameter affine motion model defined by three motion vectors; and deriving, by the one or more processors and from the values of the motion vectors of the affine motion model of the neighboring block of video data, values of predictors for motion vectors of an affine motion model of the current block of video data indicated by the second syntax element; decoding, by the one or more processors and from the encoded video bitstream, a representation of differences between the values of the motion vectors of the affine motion model for the current block of video data and the values of the predictors; determining, by the one or more processors, each of the values of the motion vectors of the affine motion model for the current block of video data from the values of the predictors and the decoded differences; determining, based on the determined values of the motion vectors of the affine motion model for the current block of video data, a predictor block of video data; and reconstructing the current block of video data based on the predictor block of video data.