Layered DCT video coder for packet switched ATM networks

A method for encoding a digital video frame f.sub.i, having N rows and M columns of pixels x.sub.i (n,m), for transmission over a digital communications channel, comprising the steps of

• selecting between an inter-frame encoding mode and an intra-frame encoding mode for differentially encoding pixels x.sub.i (n,m) of a video frame f.sub.i into corresponding differentially encoded pixels .DELTA.x.sub.i (n,m) of a difference frame .DELTA.f.sub.i, said selection being determined by the relative motion between said video frame f.sub.i and a previous video frame f.sub.i-1,
• said step of selecting between an inter-frame encoding mode and an intra-frame encoding mode further including detecting the relative motion between said video frame f.sub.i and said previous video frame f.sub.i-1, and computing a decision parameter K representing the level of detected relative motion, K being computed by
• K=k.sub.1 .DELTA.x.sub.i +k.sub.2 .sigma.
• where .DELTA.x.sub.i and .sigma..sup.2 are an estimate of the mean and variance, respectively, of difference pixel values .DELTA.x.sub.i (n,m), k1 and k2 are weighting coefficients each having a value between 0 and 1 such that k.sub.1 +k.sub.2 =1, selecting said inter-frame encoder when K<T, selecting said intra-frame encoder when K.gtoreq.T, where T represents a threshold parameter T having a value between 0 and 1,
• if said inter-frame encoding mode is selected, then encoding a said pixel x.sub.i (n,m) of frame f.sub.i into a corresponding differentially encoded pixel .DELTA.x.sub.i (n,m) of said difference frame .DELTA.f.sub.i, dependent on the corresponding pixel x.sub.i-1 (n,m) of said previous vide frame f.sub.i-1, and
• if said intra-frame encoding mode is selected, then encoding a said pixel x.sub.i (n,m) of said frame f.sub.i into a corresponding differentially encoded pixel .DELTA.x.sub.i (n,m) computed by .DELTA.x.sub.i (n,m)=x.sub.i (n,m)-x.sub.i-1 (n,m) dependent on other said pixels of the same said video frame f.sub.i,
• layer encoding said differential pixels .DELTA.x.sub.i (n,m) of frame .DELTA.f.sub.i into a plurality of separable data sets, each said data set representing video information, within a particular range of video image resolution, about said differential pixels .DELTA.x.sub.i (n,m),
• formatting said plurality of data sets, into at least one asynchronous transfer mode (ATM) packet for transmission over the digital communications channel, said ATM packet comprising a header field portion having data for establishing a virtual communications channel between selected devices on the digital communications channel, and an information field portion for transferring said plurality of data sets between said selected devices.

An apparatus for transferring a digital video frame f.sub.i, having N rows and M columns of pixels x.sub.i (n,m), for transmission over a digital communications channel, comprising

• an inter-frame encoder for encoding a said pixel x.sub.i (n,m) of a video frame f.sub.i into a corresponding differentially encoded pixel .DELTA.x.sub.i (n,m) of a difference frame .DELTA.f.sub.i dependent on the corresponding pixel x.sub.i-1 (n,m) of a previous video frame f.sub.i-1,
• an intra-frame encoder for encoding a said pixel x.sub.i (n,m) of a video frame f.sub.i into a corresponding differentially encoded pixel .DELTA.x.sub.i (n,m) dependent on other pixels of the same said frame f.sub.i,
• an encoding selector for selecting between said inter-frame encoder and said intra-frame encoder for differentially encoding pixels .DELTA.x.sub.i (n,m) of said frame f.sub.i into corresponding differentially encoded pixels .DELTA.x.sub.i (n,m) of said frame .DELTA.f.sub.i, said encoding selector being responsive to the relative motion between said video frame f.sub.i and said previous vide frame f.sub.i-1, and
• a layered resolution encoder for encoding said differential pixels .DELTA.x.sub.i (n,m) of frames .DELTA.f.sub.i into a plurality of separable data sets, each said data set representing video information, within a particular range of video image resolution, about said differential pixels .DELTA.x.sub.i (n,m),
• a packetizer for formatting said plurality of data sets into at least one asynchronous transfer mode (ATM) packet for transmission over the digital communications channel, said ATM packet comprising a header field portion having data for establishing a virtual communications channel between selected devices on the digital communications channel, and an information field portion for transferring said plurality of data sets between said selected devices,
• said information field portion having an adaptation overhead field portion including a cell sequence number for indicating the temporal relationship of said ATM packet relative to other said ATM packets, and
• a sync flag taking one of a plurality of states for indicating the composition of the remainder of said information field portion, said sync flag taking a first state when said information field portion includes a first type of information field, and a second state when said information field portion includes a second type of information field,
• said encoding selector comprises a composite frame combiner for providing a differentially encoded difference frame .DELTA.f.sub.i having a first set of pixels .DELTA.x.sub.i (n,m) encoded by said inter-frame encoder, and a second set of pixels .DELTA.x.sub.i (n,m) encoded by said intra-frame encoder, and
• said first type of information field comprises and adaptation overhead field portion further comprising
• a strip location field for indicating the location of said second set of pixels relative to said first set of pixels within said encoded difference frame .DELTA.f.sub.i.