/dev/tv
/dev/tvctl

The control device tvctl accepts the following commands to control tuning and image processing:

init

Reset the device to the default settings.

window minx miny maxx maxy

Set the display window size (default: none).

colorkey rl rh gl gh bl bh

Set the key limits for chromakey display to the given `low' and `high' values for each of red, green and blue (default: 15 63 255 15 15 63), and enable use of the colour key. The value 255 for a lower limit disables the limit.

capture minx miny maxx maxy

Set the capture window (default: none); see the description of reading the tv file, below.

capbrightness n

Set the brightness of a captured frame to n, on a scale from 0 to 100 (default: 13).

capcontrast n

Set the contrast of a captured frame to n, on a scale from 0 to 100 (default: 57).

capsaturation n

Set the saturation of a captured frame to n, on a scale from 0 to 100 (default: 51).

caphue n

Set the hue of a captured frame to n, on a scale from 0 to 100 (default: 0).

capbw n

Capture colour (n=0) or monochrome (n=1); (default: 0).

brightness n

Set the image brightness to n, on a scale from 0 to 100 (default: 0)

contrast n

Set the image contrast to n, on a scale from 0 to 100 (default: 54)

saturation n

Set image saturation to n, on a scale from 0 to 100 (default: 54)

source n

Set the input source to n (default: video input 0).

svideo n

If n is non-zero, set the input capture format to S-Video.

format n

Set the input format to n (0, NTSC-M; 1, NTSC-443; 2, external control). Default: 0.

channel c f

Sets the right frequency for HRC CATV channel c, with fine tuning by signed offset f (in MHz).

volume m[ n ]

Set the volume of left and right channels to m and n, on a scale from 0 to 100 (default: 80). If only m is given, set both left and right volumes to m.

bass n

Set the bass to n, on a scale from 0 to 100 (default: 50).

treble n

Set the treble to n, on a scale from 0 to 100 (default: 50).

freeze n

If n is non-zero, freeze the current frame; if n is zero, unfreeze the video.

The data file tv is read-only. Reading is valid only after a capture window has been set (see capture above). Each read at file offset 0 causes the contents of the input video image within the previously-set capture window to be captured. The frame data is successively returned in this and subsequent reads until a short read signals that all frame data has been transferred. The data is returned in Plan 9 picfile format, with a two line textual header followed by an empty line, followed by the image data in binary format. The header has the form:

TYPE=ccir601
WINDOW=minx miny maxx maxy

The WINDOW coordinates are those of the capture window. The image data is organised as interleaved scan lines from top to bottom of the window, with UY0 and VY1 values alternating, with two bytes per value, stored high-order byte first, encoded according to the IEEE digital component video standard.