Abstract: A video decoder compliant with the Advanced Television Systems Standard (ATSC) includes circuitry which decodes an ATSC encoded image and employs a downconversion process to produce a standard definition video signal. The video decoder includes a frequency-domain filter to reduce the resolution of the ATSC encoded signal. The video decoder downconversion system also includes a formatting section having vertical and horizontal filters, as well as resampling processing, to format the decoded and downconverted video image for a particular display and aspect ratio. The decoder senses the display format of the encoded video signal and changes the processing provided by the decoder to produce a standard definition output signal regardless of the display format of the encoded input signal. The system also includes a format converter which may be programmed to use a plurality of methods to convert the aspect ratio of the input signal for display on a display device having a different aspect ratio.

Abstract: An HDTV down conversion system including apparatus for forming a set of low resolution down-sampled pixel values corresponding to a current frame of a video signal from a set of low resolution pixel values corresponding to a residual image of a current frame of the video signal and from a set of down-sampled low resolution pixel values corresponding to reference frames of the video signal. The apparatus includes a memory for storing the set of down-sampled low resolution pixel values. An up-sampling processor receives from the memory and uses Lagrangian interpolation to convert the set of down-sampled low resolution pixel values corresponding to the reference frame of the video signal into a set of up-sampled low resolution pixel values corresponding to the reference frame of the video signal.

Abstract: A video decoder compliant with the Advanced Television Systems Standard (ATSC) includes circuitry which, when the decoder is operated in a first mode, decodes a Main Profile, High Level (MP@HL) image to produce a high-definition video output signal and decodes a Main Profile, Main Level (MP@ML) signal to produce a standard definition video signal. In addition, when the decoder is operated in a second mode, circuitry is used which generates a standard definition image from the MP@HL signal. The video decoder includes a frequency-domain filter to reduce the resolution of the MP@HL signal when the decoder is operated in the second mode.

Abstract: A video down conversion system compliant with the Advanced Television Systems Standard (ATSC) includes a decoder which decodes a Main Profile, High Level (MP@HL) image and employs a downconversion processor to produce a standard definition video signal. The system stores a subsampled image in order to reduce memory requirements and employs an upsampling filter to generate reference image data from the stored. subsampled image. The reference image data spatially correspond to the image data produced by the video decoder before it is subsampled. The upsampling filter uses different filter coefficients based on the subsampling phase of the stored image and the half-pixel indicator in the motion vector which is used to locate the downsampled reference image data in the stored subsampled image.

Abstract: A discrete cosine transform domain (DCT) filter for lowpass filtering a high resolution encoded video image represented as frequency-domain coefficient values, such as macroblocks, before decimation of the video image in the spatial domain. The DCT filter masks or weights the DCT coefficients of the video image macroblocks before processing by an inverse DCT. The filter may be implemented as a block mirror filter in the frequency domain, and the filter values may be combined with the IDCT coefficient values. Original motion vectors of the high resolution encoded video image are translated because low resolution reference images used by the decoder are not equivalent to the original high resolution images. Therefore, motion vectors are scaled to retrieve low resolution prediction blocks which are up-sampled to generate the original pixel and half-pixel values in the spatial domain.

Abstract: A transport decoder 110, for receiving and processing a transport data stream using MPEG-2 formats, includes connections to a physical layer channel interface (channel interface) 112, a buffer memory 114, a host microprocessor 116, audio and video decoders 118/120, and clock signal circuitry 122. Upon receipt of a discontinuity indicator, the transport packet headers are parsed and transport packet payloads are stored in memory. Subsequently, upon receipt of a next program counter reference (PCR) value, a counter is loaded with the received program counter reference value. Next, the data stored in memory is searched for a time stamp and, when one is found, the time stamp is retrieved. Finally, a timer interrupt is set for a point in time approximately one frame time before the time stamp value, and, when the timer interrupt occurs, the program counter reference value is sent to the decoders, thereby providing sufficient time for the decoders to process data.