A method performed in a computing device that implements a video decoder, the method comprising: receiving compressed video information in a bitstream, including: receiving one or more mode syntax elements indicating a first macroblock prediction mode for a field-coded macroblock in an interlaced bi-directionally predicted picture; evaluating the first macroblock prediction mode to determine whether the first macroblock prediction mode is forward, backward, interpolated or direct; if the first macroblock prediction mode is determined to be forward or backward, receiving a mode switch syntax element indicating that macroblock prediction mode switches from a first direction, which is one of a forward macroblock prediction mode that uses a temporal past anchor and a backward macroblock prediction mode that uses a temporal future anchor, to a second direction opposite the first direction between first and second fields of the field-coded macroblock, wherein presence of the mode switch syntax element in the bitstream following the one or more syntax elements that indicate the first macroblock prediction mode is contingent on the first macroblock prediction mode being forward or backward; decoding the interlaced bi-directionally predicted picture, including: predicting a first motion vector for the first field in the field-coded macroblock in the interlaced bi-directionally predicted picture, the first field having been encoded using the first macroblock prediction mode in the first direction; and predicting a second motion vector for the second field in the field-coded macroblock in the interlaced bi-directionally predicted picture, the second field having been encoded using a second macroblock prediction mode in the second direction opposite the first direction. receiving compressed video information in a bitstream, including: receiving one or more mode syntax elements indicating a first macroblock prediction mode for a field-coded macroblock in an interlaced bi-directionally predicted picture; evaluating the first macroblock prediction mode to determine whether the first macroblock prediction mode is forward, backward, interpolated or direct; if the first macroblock prediction mode is determined to be forward or backward, receiving a mode switch syntax element indicating that macroblock prediction mode switches from a first direction, which is one of a forward macroblock prediction mode that uses a temporal past anchor and a backward macroblock prediction mode that uses a temporal future anchor, to a second direction opposite the first direction between first and second fields of the field-coded macroblock, wherein presence of the mode switch syntax element in the bitstream following the one or more syntax elements that indicate the first macroblock prediction mode is contingent on the first macroblock prediction mode being forward or backward; receiving one or more mode syntax elements indicating a first macroblock prediction mode for a field-coded macroblock in an interlaced bi-directionally predicted picture; evaluating the first macroblock prediction mode to determine whether the first macroblock prediction mode is forward, backward, interpolated or direct; if the first macroblock prediction mode is determined to be forward or backward, receiving a mode switch syntax element indicating that macroblock prediction mode switches from a first direction, which is one of a forward macroblock prediction mode that uses a temporal past anchor and a backward macroblock prediction mode that uses a temporal future anchor, to a second direction opposite the first direction between first and second fields of the field-coded macroblock, wherein presence of the mode switch syntax element in the bitstream following the one or more syntax elements that indicate the first macroblock prediction mode is contingent on the first macroblock prediction mode being forward or backward; decoding the interlaced bi-directionally predicted picture, including: predicting a first motion vector for the first field in the field-coded macroblock in the interlaced bi-directionally predicted picture, the first field having been encoded using the first macroblock prediction mode in the first direction; and predicting a second motion vector for the second field in the field-coded macroblock in the interlaced bi-directionally predicted picture, the second field having been encoded using a second macroblock prediction mode in the second direction opposite the first direction. predicting a first motion vector for the first field in the field-coded macroblock in the interlaced bi-directionally predicted picture, the first field having been encoded using the first macroblock prediction mode in the first direction; and predicting a second motion vector for the second field in the field-coded macroblock in the interlaced bi-directionally predicted picture, the second field having been encoded using a second macroblock prediction mode in the second direction opposite the first direction.