http://v4l2spec.bytesex.org/spec/x802.htm#CAMERA-CONTROLS Video for Linux Two API Specification: Revision 0.24 Prev Chapter 1. Common API Elements Next 1.9. Extended Controls 1.9.1. Introduction The control mechanism as originally designed was meant to be used for user settings (brightness, saturation, etc). However, it turned out to be a very useful model for implementing more complicated driver APIs where each driver implements only a subset of a larger API. The MPEG encoding API was the driving force behind designing and implementing this extended control mechanism: the MPEG standard is quite large and the currently supported hardware MPEG encoders each only implement a subset of this standard. Further more, many parameters relating to how the video is encoded into an MPEG stream are specific to the MPEG encoding chip since the MPEG standard only defines the format of the resulting MPEG stream, not how the video is actually encoded into that format. Unfortunately, the original control API lacked some features needed for these new uses and so it was extended into the (not terribly originally named) extended control API. 1.9.2. The Extended Control API Three new ioctls are available: VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS and VIDIOC_TRY_EXT_CTRLS. These ioctls act on arrays of controls (as opposed to the VIDIOC_G_CTRL and VIDIOC_S_CTRL ioctls that act on a single control). This is needed since it is often required to atomically change several controls at once. Each of the new ioctls expects a pointer to a struct v4l2_ext_controls. This structure contains a pointer to the control array, a count of the number of controls in that array and a control class. Control classes are used to group similar controls into a single class. For example, control class V4L2_CTRL_CLASS_USER contains all user controls (i. e. all controls that can also be set using the old VIDIOC_S_CTRL ioctl). Control class V4L2_CTRL_CLASS_MPEG contains all controls relating to MPEG encoding, etc. All controls in the control array must belong to the specified control class. An error is returned if this is not the case. It is also possible to use an empty control array (count == 0) to check whether the specified control class is supported. The control array is a struct v4l2_ext_control array. The v4l2_ext_control structure is very similar to struct v4l2_control, except for the fact that it also allows for 64-bit values and pointers to be passed (although the latter is not yet used anywhere). It is important to realize that due to the flexibility of controls it is necessary to check whether the control you want to set actually is supported in the driver and what the valid range of values is. So use the VIDIOC_QUERYCTRL and VIDIOC_QUERYMENU ioctls to check this. Also note that it is possible that some of the menu indices in a control of type V4L2_CTRL_TYPE_MENU may not be supported (VIDIOC_QUERYMENU will return an error). A good example is the list of supported MPEG audio bitrates. Some drivers only support one or two bitrates, others support a wider range. 1.9.3. Enumerating Extended Controls The recommended way to enumerate over the extended controls is by using VIDIOC_QUERYCTRL in combination with the V4L2_CTRL_FLAG_NEXT_CTRL flag: struct v4l2_queryctrl qctrl; qctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL; while (0 == ioctl (fd, VIDIOC_QUERYCTRL, &qctrl)) { /* ... */ qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL; } The initial control ID is set to 0 ORed with the V4L2_CTRL_FLAG_NEXT_CTRL flag. The VIDIOC_QUERYCTRL ioctl will return the first control with a higher ID than the specified one. When no such controls are found an error is returned. If you want to get all controls within a specific control class, then you can set the initial qctrl.id value to the control class and add an extra check to break out of the loop when a control of another control class is found: qctrl.id = V4L2_CTRL_CLASS_MPEG | V4L2_CTRL_FLAG_NEXT_CTRL; while (0 == ioctl (fd, VIDIOC_QUERYCTRL, &qctrl)) { if (V4L2_CTRL_ID2CLASS (qctrl.id) != V4L2_CTRL_CLASS_MPEG) break; /* ... */ qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL; } The 32-bit qctrl.id value is subdivided into three bit ranges: the top 4 bits are reserved for flags (e. g. V4L2_CTRL_FLAG_NEXT_CTRL) and are not actually part of the ID. The remaining 28 bits form the control ID, of which the most significant 12 bits define the control class and the least significant 16 bits identify the control within the control class. It is guaranteed that these last 16 bits are always non-zero for controls. The range of 0x1000 and up are reserved for driver-specific controls. The macro V4L2_CTRL_ID2CLASS(id) returns the control class ID based on a control ID. If the driver does not support extended controls, then VIDIOC_QUERYCTRL will fail when used in combination with V4L2_CTRL_FLAG_NEXT_CTRL. In that case the old method of enumerating control should be used (see 1.8). But if it is supported, then it is guaranteed to enumerate over all controls, including driver-private controls. 1.9.4. Creating Control Panels It is possible to create control panels for a graphical user interface where the user can select the various controls. Basically you will have to iterate over all controls using the method described above. Each control class starts with a control of type V4L2_CTRL_TYPE_CTRL_CLASS. VIDIOC_QUERYCTRL will return the name of this control class which can be used as the title of a tab page within a control panel. The flags field of struct v4l2_queryctrl also contains hints on the behavior of the control. See the VIDIOC_QUERYCTRL documentation for more details. 1.9.5. MPEG Control Reference Below all controls within the MPEG control class are described. First the generic controls, then controls specific for certain hardware. 1.9.5.1. Generic MPEG Controls Table 1-2. MPEG Control IDs ID Type Description V4L2_CID_MPEG_CLASS class The MPEG class descriptor. Calling VIDIOC_QUERYCTRL for this control will return a description of this control class. This description can be used as the caption of a Tab page in a GUI, for example. V4L2_CID_MPEG_STREAM_TYPE enum The MPEG-1, -2 or -4 output stream type. One cannot assume anything here. Each hardware MPEG encoder tends to support different subsets of the available MPEG stream types. The currently defined stream types are: V4L2_MPEG_STREAM_TYPE_MPEG2_PS MPEG-2 program stream V4L2_MPEG_STREAM_TYPE_MPEG2_TS MPEG-2 transport stream V4L2_MPEG_STREAM_TYPE_MPEG1_SS MPEG-1 system stream V4L2_MPEG_STREAM_TYPE_MPEG2_DVD MPEG-2 DVD-compatible stream V4L2_MPEG_STREAM_TYPE_MPEG1_VCD MPEG-1 VCD-compatible stream V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD MPEG-2 SVCD-compatible stream V4L2_CID_MPEG_STREAM_PID_PMT integer Program Map Table Packet ID for the MPEG transport stream (default 16) V4L2_CID_MPEG_STREAM_PID_AUDIO integer Audio Packet ID for the MPEG transport stream (default 256) V4L2_CID_MPEG_STREAM_PID_VIDEO integer Video Packet ID for the MPEG transport stream (default 260) V4L2_CID_MPEG_STREAM_PID_PCR integer Packet ID for the MPEG transport stream carrying PCR fields (default 259) V4L2_CID_MPEG_STREAM_PES_ID_AUDIO integer Audio ID for MPEG PES V4L2_CID_MPEG_STREAM_PES_ID_VIDEO integer Video ID for MPEG PES V4L2_CID_MPEG_STREAM_VBI_FMT enum Some cards can embed VBI data (e. g. Closed Caption, Teletext) into the MPEG stream. This control selects whether VBI data should be embedded, and if so, what embedding method should be used. The list of possible VBI formats depends on the driver. The currently defined VBI format types are: V4L2_MPEG_STREAM_VBI_FMT_NONE No VBI in the MPEG stream V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI in private packets, IVTV format (documented in the kernel sources in the file Documentation/video4linux/cx2341x/README.vbi) V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ enum MPEG Audio sampling frequency. Possible values are: V4L2_MPEG_AUDIO_SAMPLING_FREQ_44100 44.1 kHz V4L2_MPEG_AUDIO_SAMPLING_FREQ_48000 48 kHz V4L2_MPEG_AUDIO_SAMPLING_FREQ_32000 32 kHz V4L2_CID_MPEG_AUDIO_ENCODING enum MPEG Audio encoding. Possible values are: V4L2_MPEG_AUDIO_ENCODING_LAYER_1 MPEG Layer I encoding V4L2_MPEG_AUDIO_ENCODING_LAYER_2 MPEG Layer II encoding V4L2_MPEG_AUDIO_ENCODING_LAYER_3 MPEG Layer III encoding V4L2_CID_MPEG_AUDIO_L1_BITRATE enum Layer I bitrate. Possible values are: V4L2_MPEG_AUDIO_L1_BITRATE_32K 32 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_64K 64 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_96K 96 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_128K 128 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_160K 160 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_192K 192 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_224K 224 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_256K 256 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_288K 288 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_320K 320 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_352K 352 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_384K 384 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_416K 416 kbit/s V4L2_MPEG_AUDIO_L1_BITRATE_448K 448 kbit/s V4L2_CID_MPEG_AUDIO_L2_BITRATE enum Layer II bitrate. Possible values are: V4L2_MPEG_AUDIO_L2_BITRATE_32K 32 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_48K 48 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_56K 56 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_64K 64 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_80K 80 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_96K 96 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_112K 112 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_128K 128 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_160K 160 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_192K 192 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_224K 224 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_256K 256 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_320K 320 kbit/s V4L2_MPEG_AUDIO_L2_BITRATE_384K 384 kbit/s V4L2_CID_MPEG_AUDIO_L3_BITRATE enum Layer III bitrate. Possible values are: V4L2_MPEG_AUDIO_L3_BITRATE_32K 32 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_40K 40 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_48K 48 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_56K 56 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_64K 64 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_80K 80 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_96K 96 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_112K 112 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_128K 128 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_160K 160 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_192K 192 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_224K 224 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_256K 256 kbit/s V4L2_MPEG_AUDIO_L3_BITRATE_320K 320 kbit/s V4L2_CID_MPEG_AUDIO_MODE enum MPEG Audio mode. Possible values are: V4L2_MPEG_AUDIO_MODE_STEREO Stereo V4L2_MPEG_AUDIO_MODE_JOINT_STEREO Joint Stereo V4L2_MPEG_AUDIO_MODE_DUAL Bilingual V4L2_MPEG_AUDIO_MODE_MONO Mono V4L2_CID_MPEG_AUDIO_MODE_EXTENSION enum Joint Stereo audio mode extension. In Layer I and II they indicate which subbands are in intensity stereo. All other subbands are coded in stereo. Layer III is not (yet) supported. Possible values are: V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_4 Subbands 4-31 in intensity stereo V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_8 Subbands 8-31 in intensity stereo V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_12 Subbands 12-31 in intensity stereo V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_16 Subbands 16-31 in intensity stereo V4L2_CID_MPEG_AUDIO_EMPHASIS enum Audio Emphasis. Possible values are: V4L2_MPEG_AUDIO_EMPHASIS_NONE None V4L2_MPEG_AUDIO_EMPHASIS_50_DIV_15_uS 50/15 microsecond emphasis V4L2_MPEG_AUDIO_EMPHASIS_CCITT_J17 CCITT J.17 V4L2_CID_MPEG_AUDIO_CRC enum CRC method. Possible values are: V4L2_MPEG_AUDIO_CRC_NONE None V4L2_MPEG_AUDIO_CRC_CRC16 16 bit parity check V4L2_CID_MPEG_AUDIO_MUTE bool Mutes the audio when capturing. This is not done by muting audio hardware, which can still produce a slight hiss, but in the encoder itself, guaranteeing a fixed and reproducable audio bitstream. 0 = unmuted, 1 = muted. V4L2_CID_MPEG_VIDEO_ENCODING enum MPEG Video encoding method. Possible values are: V4L2_MPEG_VIDEO_ENCODING_MPEG_1 MPEG-1 Video encoding V4L2_MPEG_VIDEO_ENCODING_MPEG_2 MPEG-2 Video encoding V4L2_CID_MPEG_VIDEO_ASPECT enum Video aspect. Possible values are: V4L2_MPEG_VIDEO_ASPECT_1x1 V4L2_MPEG_VIDEO_ASPECT_4x3 V4L2_MPEG_VIDEO_ASPECT_16x9 V4L2_MPEG_VIDEO_ASPECT_221x100 V4L2_CID_MPEG_VIDEO_B_FRAMES integer Number of B-Frames (default 2) V4L2_CID_MPEG_VIDEO_GOP_SIZE integer GOP size (default 12) V4L2_CID_MPEG_VIDEO_GOP_CLOSURE bool GOP closure (default 1) V4L2_CID_MPEG_VIDEO_PULLDOWN bool Enable 3:2 pulldown (default 0) V4L2_CID_MPEG_VIDEO_BITRATE_MODE enum Video bitrate mode. Possible values are: V4L2_MPEG_VIDEO_BITRATE_MODE_VBR Variable bitrate V4L2_MPEG_VIDEO_BITRATE_MODE_CBR Constant bitrate V4L2_CID_MPEG_VIDEO_BITRATE integer Video bitrate in bits per second. V4L2_CID_MPEG_VIDEO_BITRATE_PEAK integer Peak video bitrate in bits per second. Must be larger or equal to the average video bitrate. It is ignored if the video bitrate mode is set to constant bitrate. V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION integer For every captured frame, skip this many subsequent frames (default 0). V4L2_CID_MPEG_VIDEO_MUTE bool "Mutes" the video to a fixed color when capturing. This is useful for testing, to produce a fixed video bitstream. 0 = unmuted, 1 = muted. V4L2_CID_MPEG_VIDEO_MUTE_YUV integer Sets the "mute" color of the video. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit): Bit 0:7 V chrominance information Bit 8:15 U chrominance information Bit 16:23 Y luminance information Bit 24:31 Must be zero. 1.9.5.2. CX2341x MPEG Controls The following MPEG class controls deal with MPEG encoding settings that are specific to the Conexant CX23415 and CX23416 MPEG encoding chips. Table 1-3. CX2341x Control IDs ID Type Description V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE enum Sets the Spatial Filter mode (default MANUAL). Possible values are: V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_MANUAL Choose the filter manually V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_AUTO Choose the filter automatically V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER integer (0-15) The setting for the Spatial Filter. 0 = off, 15 = maximum. (Default is 0.) V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE enum Select the algorithm to use for the Luma Spatial Filter (default 1D_HOR). Possible values: V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_OFF No filter V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_HOR One-dimensional horizontal V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_VERT One-dimensional vertical V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_HV_SEPARABLE Two-dimensional separable V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_SYM_NON_SEPARABLE Two-dimensional symmetrical non-separable V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE enum Select the algorithm for the Chroma Spatial Filter (default 1D_HOR). Possible values are: V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_OFF No filter V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_1D_HOR One-dimensional horizontal V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE enum Sets the Temporal Filter mode (default MANUAL). Possible values are: V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_MANUAL Choose the filter manually V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_AUTO Choose the filter automatically V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER integer (0-31) The setting for the Temporal Filter. 0 = off, 31 = maximum. (Default is 8 for full-scale capturing and 0 for scaled capturing.) V4L2_CID_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE enum Median Filter Type (default OFF). Possible values are: V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_OFF No filter V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR Horizontal filter V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_VERT Vertical filter V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR_VERT Horizontal and vertical filter V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_DIAG Diagonal filter V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_BOTTOM integer (0-255) Threshold above which the luminance median filter is enabled (default 0) V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_TOP integer (0-255) Threshold below which the luminance median filter is enabled (default 255) V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_BOTTOM integer (0-255) Threshold above which the chroma median filter is enabled (default 0) V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_TOP integer (0-255) Threshold below which the chroma median filter is enabled (default 255) V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS bool The CX2341X MPEG encoder can insert one empty MPEG-2 PES packet into the stream between every four video frames. The packet size is 2048 bytes, including the packet_start_code_prefix and stream_id fields. The stream_id is 0xBF (private stream 2). The payload consists of 0x00 bytes, to be filled in by the application. 0 = do not insert, 1 = insert packets. 1.9.6. Camera Control Reference The Camera class includes controls for mechanical (or equivalent digital) features of a device such as controllable lenses or sensors. Table 1-4. Camera Control IDs ID Type Description V4L2_CID_CAMERA_CLASS class The Camera class descriptor. Calling VIDIOC_QUERYCTRL for this control will return a description of this control class. V4L2_CID_EXPOSURE_AUTO integer Enables automatic adjustments of the exposure time and/or iris aperture. The effect of manual changes of the exposure time or iris aperture while these features are enabled is undefined, drivers should ignore such requests. Possible values are: V4L2_EXPOSURE_AUTO Automatic exposure time, automatic iris aperture. V4L2_EXPOSURE_MANUAL Manual exposure time, manual iris. V4L2_EXPOSURE_SHUTTER_PRIORITY Manual exposure time, auto iris. V4L2_EXPOSURE_APERTURE_PRIORITY Auto exposure time, manual iris. V4L2_CID_EXPOSURE_ABSOLUTE integer Determines the exposure time of the camera sensor. The exposure time is limited by the frame interval. Drivers should interpret the values as 100 µs units, where the value 1 stands for 1/10000th of a second, 10000 for 1 second and 100000 for 10 seconds. V4L2_CID_EXPOSURE_AUTO_PRIORITY boolean When V4L2_CID_EXPOSURE_AUTO is set to AUTO or SHUTTER_PRIORITY, this control determines if the device may dynamically vary the frame rate. By default this feature is disabled (0) and the frame rate must remain constant. V4L2_CID_PAN_RELATIVE integer This control turns the camera horizontally by the specified amount. The unit is undefined. A positive value moves the camera to the right (clockwise when viewed from above), a negative value to the left. A value of zero does not cause motion. V4L2_CID_TILT_RELATIVE integer This control turns the camera vertically by the specified amount. The unit is undefined. A positive value moves the camera up, a negative value down. A value of zero does not cause motion. V4L2_CID_PAN_RESET boolean When this control is set to TRUE (1), the camera moves horizontally to the default position. V4L2_CID_TILT_RESET boolean When this control is set to TRUE (1), the camera moves vertically to the default position. V4L2_CID_PAN_ABSOLUTE integer This control turns the camera horizontally to the specified position. Positive values move the camera to the right (clockwise when viewed from above), negative values to the left. Drivers should interpret the values as arc seconds, with valid values between -180 * 3600 and +180 * 3600 inclusive. V4L2_CID_TILT_ABSOLUTE integer This control turns the camera vertically to the specified position. Positive values move the camera up, negative values down. Drivers should interpret the values as arc seconds, with valid values between -180 * 3600 and +180 * 3600 inclusive. V4L2_CID_FOCUS_ABSOLUTE integer This control sets the focal point of the camera to the specified position. The unit is undefined. Positive values set the focus closer to the camera, negative values towards infinity. V4L2_CID_FOCUS_RELATIVE integer This control moves the focal point of the camera by the specified amount. The unit is undefined. Positive values move the focus closer to the camera, negative values towards infinity. V4L2_CID_FOCUS_AUTO boolean Enables automatic focus adjustments. The effect of manual focus adjustments while this feature is enabled is undefined, drivers should ignore such requests. Prev Home Next User Controls Up Data Formats