Method and apparatus for the selection of data for use in VTR trick playback operation in a system using intra-coded video frames

DETAILED DESCRIPTION The present invention is directed to data extraction techniques and, more particularly, to a method and apparatus for extracting intra-coded video frames from a digital video bitstream and for processing the selected intra-coded video frames to generate intra-coded video frames suitable for use during video tape recorder ("VTR") trick play operation.
In accordance with the present invention, the generated intra-coded video frames can be recorded on a tape and later read back during VTR trick play operation to provide sufficient data to produce recognizable images or portions of images during trick play operation.
Selection of intra-coded video frames from a received bitstream of video data is easiest when a fixed size of GOPs is used and the size of the GOPs is known.
In such a case, I-frames will arrive in the bitstream in a predictable manner.
By selecting a trick play speed that corresponds to the interval between I- frames, selection of the I-frames for trick play operation becomes straight forward with each received I-frame being selected for recording and later playback during trick play operation.
For example, if the GOP size were 7 and the trick play speed to be supported was 7x, each received I-frame can be selected and used for trick play operation.
Similarly, where the trick play speed is an integer multiple of a GOP size, in a system which has a single GOP size, it is easy to select received I-frames for trick play use.
For example, if the GOP size is fixed at 7 and the trick play speed to be supported is 14x, one can select every other received I-frame for recording in trick play tape segments on a tape corresponding to a 14x fast scan track.
In accordance with one embodiment of the present invention, where the GOP size is N and the speed up rate is M, every M/N received I-frames are selected for use during Mx trick play operation, where M and N are integers such that M/N is also an integer.
However, MPEG-2 does not require that GOP's be of a fixed size