4.16. Metadata Interface¶
Metadata refers to any non-image data that supplements video frames with additional information. This may include statistics computed over the image or frame capture parameters supplied by the image source. This interface is intended for transfer of metadata to userspace and control of that operation.
The metadata interface is implemented on video capture device nodes. The device can be dedicated to metadata or can implement both video and metadata capture as specified in its reported capabilities.
4.16.1. Querying Capabilities¶
Device nodes supporting the metadata interface set the V4L2_CAP_META_CAPTURE
flag in the device_caps field of the
v4l2_capability structure returned by the VIDIOC_QUERYCAP()
ioctl. That flag means the device can capture metadata to memory.
At least one of the read/write or streaming I/O methods must be supported.
4.16.2. Data Format Negotiation¶
The metadata device uses the Data Formats ioctls to select the capture format.
The metadata buffer content format is bound to that selected format. In addition
to the basic Data Formats ioctls, the VIDIOC_ENUM_FMT() ioctl must be
supported as well.
To use the Data Formats ioctls applications set the type field of the
v4l2_format structure to V4L2_BUF_TYPE_META_CAPTURE and use the
v4l2_meta_format meta member of the fmt union as needed per
the desired operation. Both drivers and applications must set the remainder of
the v4l2_format structure to 0.
| __u32 | dataformat |
The data format, set by the application. This is a little endian four character code. V4L2 defines metadata formats in Metadata Formats. |
| __u32 | buffersize |
Maximum buffer size in bytes required for data. The value is set by the driver. |