Re: [RFC] Motion Detection API

Laurent Pinchart
2013-04-29T20:52:25Z

Hi Hans,

Sorry for the late reply.

On Friday 12 April 2013 17:36:16 Hans Verkuil wrote:
> This RFC looks at adding support for motion detection to V4L2. This is the
> main missing piece that prevents the go7007 and solo6x10 drivers from being
> moved into mainline from the staging directory.
>
> Step one is to look at existing drivers/hardware:
>
> 1) The go7007 driver:
>
> - divides the frame into blocks of 16x16 pixels each (that's 45x36 blocks
> for PAL)
> - each block can be assigned to region 0, 1, 2 or 3
> - each region has:
> - a pixel change threshold
> - a motion vector change threshold
> - a trigger level; if this is 0, then motion detection for this
> region is disabled
> - when streaming the reserved field of v4l2_buffer is used as a bitmask:
> one bit for each region where motion is detected.
>
> 2) The solo6x10 driver:
>
> - divides the frame into blocks of 16x16 pixels each
> - each block has its own threshold
> - the driver adds one MOTION_ON buffer flag and one MOTION_DETECTED
> buffer flag.
> - motion detection can be disabled or enabled.
> - the driver has a global motion detection mode with just one threshold:
> in that case all blocks are set to the same threshold.
> - there is also support for displaying a border around the image if
> motion is detected (very hardware specific).
>
> 3) The tw2804 video encoder (based on the datasheet, not implemented in the
> driver):
>
> - divides the image in 12x12 blocks (block size will differ for NTSC vs
> PAL)
> - motion detection can be enabled or disabled for each block
> - there are four controls:
> - luminance level change threshold
> - spatial sensitivity threshold
> - temporal sensitivity threshold
> - velocity control (determines how well slow motions are detected)
> - detection is reported by a hardware pin in this case
>
> Comparing these three examples of motion detection I see quite a lot of
> similarities, enough to make a proposal for an API:
>
> - Add a MOTION_DETECTION menu control:
> - Disabled
> - Global Motion Detection
> - Regional Motion Detection
>
> If 'Global Motion Detection' is selected, then various threshold controls
> become available. What sort of thresholds are available seems to be quite
> variable, so I am inclined to leave this as private controls.
>
> - Add new buffer flags when motion is detected. The go7007 driver would need
> 4 bits (one for each region), the others just one. This can be done by
> taking 4 bits from the v4l2_buffer flags field. There are still 16 bits
> left there, and if it becomes full, then we still have two reserved fields.
> I see no reason for adding a 'MOTION_ON' flag as the solo6x10 driver does
> today: just check the MOTION_DETECTION control if you want to know if
> motion detection is on or not.

We're really starting to shove metadata in buffer flags. Isn't it time to add
a proper metadata API ? I don't really like the idea of using (valuable)
buffer flags for a feature supported by three drivers only.

> - Add two new ioctls to get and set the block data:
>
> #define V4L2_MD_HOR_BLOCKS (64)
> #define V4L2_MD_VERT_BLOCKS (48)
>
> #define V4L2_MD_TYPE_REGION (1)
> #define V4L2_MD_TYPE_THRESHOLD (2)
>
> struct v4l2_md_blocks {
> __u32 type;
> struct v4l2_rect rect;
> __u32 minimum;
> __u32 maximum;
> __u32 reserved[32];
> __u16 blocks[V4L2_MD_HOR_BLOCKS][V4L2_MD_VERT_BLOCKS];
> };
>
> #define VIDIOC_G_MD_BLOCKS _IORW('V', 103, struct v4l2_md_blocks)
> #define VIDIOC_S_MD_BLOCKS _IORW('V', 104, struct v4l2_md_blocks)
>
> Apps must fill in type, then can call G_MD_BLOCKS to get the current block
> values for that type. TYPE_REGION returns to which region each block
> belongs, TYPE_THRESHOLD returns threshold values for each block.
>
> rect returns the rectangle of valid blocks, minimum and maximum the min
> and max values for each 'blocks' array element.
>
> To change the blocks apps call S_MD_BLOCKS, fill in type, rect (rect is
> useful here to set only a subset of all blocks) and blocks.
>
> So the go7007 would return 45x36 in rect, type would be REGION, min/max
> would be 0-3.
>
> solo6x10 would return 45x36 in rect, type would be THRESHOLD, min/max would
> be 0-65535.
>
> TW2804 would return 12x12 in rect, type would be THRESHOLD, min/max would be
> 0-1.
>
> Comment? Questions?

--
Regards,

Laurent Pinchart