diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DocBook/media/v4l/io.xml | 54 |
1 files changed, 36 insertions, 18 deletions
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml index 49e48be9c2b4..0a5d8c6003cf 100644 --- a/Documentation/DocBook/media/v4l/io.xml +++ b/Documentation/DocBook/media/v4l/io.xml @@ -676,10 +676,11 @@ plane structures.</para> <entry>__u32</entry> <entry><structfield>index</structfield></entry> <entry></entry> - <entry>Number of the buffer, set by the application. This -field is only used for <link linkend="mmap">memory mapping</link> I/O -and can range from zero to the number of buffers allocated -with the &VIDIOC-REQBUFS; ioctl (&v4l2-requestbuffers; <structfield>count</structfield>) minus one.</entry> + <entry>Number of the buffer, set by the application except +when calling &VIDIOC-DQBUF;, then it is set by the driver. +This field can range from zero to the number of buffers allocated +with the &VIDIOC-REQBUFS; ioctl (&v4l2-requestbuffers; <structfield>count</structfield>), +plus any buffers allocated with &VIDIOC-CREATE-BUFS; minus one.</entry> </row> <row> <entry>__u32</entry> @@ -698,7 +699,7 @@ linkend="v4l2-buf-type" /></entry> buffer. It depends on the negotiated data format and may change with each buffer for compressed variable size data like JPEG images. Drivers must set this field when <structfield>type</structfield> -refers to an input stream, applications when an output stream.</entry> +refers to an input stream, applications when it refers to an output stream.</entry> </row> <row> <entry>__u32</entry> @@ -715,7 +716,7 @@ linkend="buffer-flags" />.</entry> buffer, see <xref linkend="v4l2-field" />. This field is not used when the buffer contains VBI data. Drivers must set it when <structfield>type</structfield> refers to an input stream, -applications when an output stream.</entry> +applications when it refers to an output stream.</entry> </row> <row> <entry>struct timeval</entry> @@ -729,7 +730,9 @@ applications when an output stream.</entry> stores the time at which the last data byte was actually sent out in the <structfield>timestamp</structfield> field. This permits applications to monitor the drift between the video and system - clock.</para></entry> + clock. For output streams that use <constant>V4L2_BUF_FLAG_TIMESTAMP_COPY</constant> + the application has to fill in the timestamp which will be copied + by the driver to the capture stream.</para></entry> </row> <row> <entry>&v4l2-timecode;</entry> @@ -822,7 +825,8 @@ is the file descriptor associated with a DMABUF buffer.</entry> <entry><structfield>length</structfield></entry> <entry></entry> <entry>Size of the buffer (not the payload) in bytes for the - single-planar API. For the multi-planar API the application sets + single-planar API. This is set by the driver based on the calls to + &VIDIOC-REQBUFS; and/or &VIDIOC-CREATE-BUFS;. For the multi-planar API the application sets this to the number of elements in the <structfield>planes</structfield> array. The driver will fill in the actual number of valid elements in that array. @@ -856,13 +860,15 @@ should set this to 0.</entry> <entry><structfield>bytesused</structfield></entry> <entry></entry> <entry>The number of bytes occupied by data in the plane - (its payload).</entry> + (its payload). Drivers must set this field when <structfield>type</structfield> + refers to an input stream, applications when it refers to an output stream.</entry> </row> <row> <entry>__u32</entry> <entry><structfield>length</structfield></entry> <entry></entry> - <entry>Size in bytes of the plane (not its payload).</entry> + <entry>Size in bytes of the plane (not its payload). This is set by the driver + based on the calls to &VIDIOC-REQBUFS; and/or &VIDIOC-CREATE-BUFS;.</entry> </row> <row> <entry>union</entry> @@ -901,7 +907,9 @@ should set this to 0.</entry> <entry>__u32</entry> <entry><structfield>data_offset</structfield></entry> <entry></entry> - <entry>Offset in bytes to video data in the plane, if applicable. + <entry>Offset in bytes to video data in the plane. + Drivers must set this field when <structfield>type</structfield> + refers to an input stream, applications when it refers to an output stream. </entry> </row> <row> @@ -1031,7 +1039,7 @@ buffer cannot be on both queues at the same time, the <constant>V4L2_BUF_FLAG_QUEUED</constant> and <constant>V4L2_BUF_FLAG_DONE</constant> flag are mutually exclusive. They can be both cleared however, then the buffer is in "dequeued" -state, in the application domain to say so.</entry> +state, in the application domain so to say.</entry> </row> <row> <entry><constant>V4L2_BUF_FLAG_ERROR</constant></entry> @@ -1049,27 +1057,35 @@ state, in the application domain to say so.</entry> <entry>Drivers set or clear this flag when calling the <constant>VIDIOC_DQBUF</constant> ioctl. It may be set by video capture devices when the buffer contains a compressed image which is a -key frame (or field), &ie; can be decompressed on its own.</entry> +key frame (or field), &ie; can be decompressed on its own. Also know as +an I-frame. Applications can set this bit when <structfield>type</structfield> +refers to an output stream.</entry> </row> <row> <entry><constant>V4L2_BUF_FLAG_PFRAME</constant></entry> <entry>0x00000010</entry> <entry>Similar to <constant>V4L2_BUF_FLAG_KEYFRAME</constant> this flags predicted frames or fields which contain only differences to a -previous key frame.</entry> +previous key frame. Applications can set this bit when <structfield>type</structfield> +refers to an output stream.</entry> </row> <row> <entry><constant>V4L2_BUF_FLAG_BFRAME</constant></entry> <entry>0x00000020</entry> - <entry>Similar to <constant>V4L2_BUF_FLAG_PFRAME</constant> - this is a bidirectional predicted frame or field. [ooc tbd]</entry> + <entry>Similar to <constant>V4L2_BUF_FLAG_KEYFRAME</constant> +this flags a bi-directional predicted frame or field which contains only +the differences between the current frame and both the preceding and following +key frames to specify its content. Applications can set this bit when +<structfield>type</structfield> refers to an output stream.</entry> </row> <row> <entry><constant>V4L2_BUF_FLAG_TIMECODE</constant></entry> <entry>0x00000100</entry> <entry>The <structfield>timecode</structfield> field is valid. Drivers set or clear this flag when the <constant>VIDIOC_DQBUF</constant> -ioctl is called.</entry> +ioctl is called. Applications can set this bit and the corresponding +<structfield>timecode</structfield> structure when <structfield>type</structfield> +refers to an output stream.</entry> </row> <row> <entry><constant>V4L2_BUF_FLAG_PREPARED</constant></entry> @@ -1141,7 +1157,9 @@ in which case caches have not been used.</entry> the frame. Logical 'and' operation between the <structfield>flags</structfield> field and <constant>V4L2_BUF_FLAG_TSTAMP_SRC_MASK</constant> produces the - value of the timestamp source.</entry> + value of the timestamp source. Applications must set the timestamp + source when <structfield>type</structfield> refers to an output stream + and <constant>V4L2_BUF_FLAG_TIMESTAMP_COPY</constant> is set.</entry> </row> <row> <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_EOF</constant></entry> |