H.261 Attributes

These attributes are specific to SunVideo Plus when used in conjunction with H.261 compression or decompression. They have no effect if not performing hardware-based compression or decompression.

H261_BIT_RATE

This attribute sets the desired maximum compression bit rate. The rate is in bits per second of units of 1000. For example, the default value of 256 produces a maximum bit rate of 256000 bits per second (32000 bytes/sec).

Access: set/get Type: int (in kbits/sec) Default: 256

H261_MAX_QUANT

This attribute sets the desired maximum quantization. As the quantization factor is lowered, the compressed image quality improves. Since a lower quantization generally results in an increase in bits-per-image, the frame rate for a given bit rate can decrease. The opposite is true for increasing quantization.

Access: set/get Type: int (range: 1 to 31) Default: 10

H261_IBLOCK_REFRESH

This attribute sets the desired period in milliseconds before the compressor should update a given H261 macroblock with an intra-encoded block. H261 requires that each macroblock be encoded as an intra-encoded block every 132 frames. If compressing at 10 fps, this implies that a given block may not be intra-encoded for up to 13 seconds. On a lossy network, a loss of a frame results visually in distorted blocks in the decompressed image. Waiting for up to 13 seconds for these bad blocks to refresh is probably not acceptable. The purpose of this attribute is to speed up the refresh of macroblocks during lossy transmission of H261 streams over networks.

Access: set/get Type: int Default: 1500 (msec)

H261_FUR

Setting this flag issues a fast update request to the H.261 compressor. The fast update is basically the request for an intra/key frame.

Access: set/get Type: XIL_boolean Default: FALSE

H261_PIP

This flag tells the H.261 decoder to inlay a picture of the local view in the top-left corner of the decompressed image. If not performing hardware compression, the pip image is gray.

Access: set/get Type: XIL_boolean Default: FALSE

HW_DECOMPRESS_CIS

This attribute selects which CIS hardware accelerated decompression should be performed on. The default value of NULL implies that the first CIS encountered by a decompression molecule is targeted for hardware accelerated decompression. Once a CIS has been selected, any other CIS encountered by hardware decompression molecules will be rejected and the decompression will occur through the appropriate XIL software decoder. A value of -1 is a good value to use to disable hardware-based decompression.

Because XIL has no mechanism for informing the decompressor when a CIS is destroyed, this attribute must also be set in order to perform hardware accelerated decompression on a new CIS.

Access: set/get Type: XilCis Default: NULL