6 233 392

6,233,392 Title:

Constrained encoded motion vectors

A storage medium has recorded thereon a packetized digitally encoded image representative signal for forward and reverse direction reproduction. The digitally encoded signal comprises a plurality of groups of pictures, a group of the plurality of groups including at least an intra coded picture and a predicted picture. The intra coded picture type and the predicted picture type each comprise top and bottom fields. The predicted picture type has a first motion vector for decoding in the forward direction, and has a second motion vector for decoding in the reverse direction. In a further inventive arrangement a storage medium has recorded thereon a packetized digitally encoded image representative signal for forward and reverse direction reproduction. The digitally encoded signal comprises a plurality of groups of pictures, a group of said plurality of groups including at least an intra coded picture and a predicted picture. The intra coded picture and the predicted picture comprise a top field and a bottom field. The digitally encoded signal comprises. A motion vector for constructing the predicted picture from a predetermined only one of the top and bottom fields.

What is claimed is:

1. A method for recording on a storage medium a packetized digitally encoded image representative signal for reproduction in normal and trick modes, said method comprising thefollowing steps:

encoding a video signal as a plurality of groups of pictures, wherein a group of said plurality of groups including at least an intra coded picture and a predicted picture;

said intra coded picture and said predicted picture having first and second fields;

deriving a motion vector from only one of said fields of said intra coded picture for constructing said predicted picture during said trick mode; and,

recording said plurality of groups of pictures and said motion vector on said storage medium.

2. The method of claim 1, wherein said deriving step includes a step of;

selecting a preceding intra coded picture for deriving said motion vector for constructing said predicted picture during said normal mode.

3. The method of claim 1, wherein said recording step includes;

recording said motion vector derived from only one of said fields as part of picture user data contained in said packetized digitally encoded image representative signal.

4. The method of claim 1, wherein said deriving step includes a step of;

selecting a bottom field as said only one of said fields of said intra coded picture.

5. The method of claim 1, wherein said encoding step includes the step of;

originating said video signal from film.

6. An apparatus for reproducing a digitally encoded signal from a medium, comprising:

a source of said digitally encoded signal representative of a plurality of groups of pictures, a group of said plurality of groups including at least one intra coded picture type and at least one predictively coded picture type and motioncompensation data;

said motion compensation data being representative of a single field of one of the two picture types; and,

a decoder coupled to said source for decoding the two types of pictures, wherein reverse direction reproduction of said at least one predictively coded picture type is decoded responsive to motion compensation data representative of said singlefield of said one of said two picture types from a preceding group of pictures of said plurality of groups of pictures.

7. The reproducing apparatus of claim 6, wherein said single field is a bottom field.

8. An apparatus for processing a digitally encoded signal, comprising:

a source of said digitally encoded signal representative of a plurality of groups of pictures, a group of said plurality of groups arranged in a sequence including at least one I type and at least one P type picture and motion compensation data;

said motion compensation data indicating a prediction image part for decoding said one P type picture; and,

a decoder coupled to said source for decoding said I type and P type pictures, wherein a forward play first mode said P type picture decoding is responsive to said prediction image part being represented by a picture, and in a trick play secondmode said one P type picture decoding is responsive to said prediction image part being represented by a single field of said picture.

9. The processing apparatus of claim 8, wherein said single field is a bottom field.

10. The processing apparatus of claim 8 wherein said second mode said motion compensation data is part of picture user data contained in said packetized digitally encoded image representative signal.