* Query the meaning of variable in v4l2_pix_format and v4l2_plane @ 2011-11-04 13:07 Jonghun Han 2011-11-04 13:28 ` Marek Szyprowski 2011-11-04 16:02 ` Tomasz Stanislawski 0 siblings, 2 replies; 4+ messages in thread From: Jonghun Han @ 2011-11-04 13:07 UTC (permalink / raw) To: linux-media; +Cc: m.szyprowski Hi, I'm not sure the meaning of variables in v4l2_pix_format and v4l2_plane. Especially bytesperline, sizeimage, length and bytesused. v4l2_pix_format.width = width v4l2_pix_format.height = height v4l2_pix_format.bytesperline = bytesperline [in bytes] v4l2_pix_format.sizeimage = bytesperline * buf height -> Is this right ? v4l2_plane.length = bytesperline * buf height -> Is this right ? I don't which is right. v4l2_plane.bytesused = bytesperline * (top + height) v4l2_plane.bytesused = bytesperline * height v4l2_plane.bytesused = width * height * bytesperpixel v4l2_plane.bytesused = bytesperline * (top + height) - (pixelperline - (left + width)) * bytesperpixel I assumed the following buffer. | | |<--------------------- bytesperline --------------------->| | | +----------------------------------------------------------+----- | ^ | ^ | | | | | | | | t | | | o | | | p | | | | | | | | | | V |<--------- width ---------->| | | |<-- left -->+----------------------------+ - | | | | | ^ | | | | | | b | | | | | u | | | | f | | | h | | | | e | h | | | i | e | | | g | i | | | h | g | | | t | h | | | | t | | | | | | | | | | | | | | v | | | +----------------------------+ - | | | | | | | | | | v +----------------------------------------------------------+----- Best regards, ^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: Query the meaning of variable in v4l2_pix_format and v4l2_plane 2011-11-04 13:07 Query the meaning of variable in v4l2_pix_format and v4l2_plane Jonghun Han @ 2011-11-04 13:28 ` Marek Szyprowski 2011-11-04 14:48 ` Hans Verkuil 2011-11-04 16:02 ` Tomasz Stanislawski 1 sibling, 1 reply; 4+ messages in thread From: Marek Szyprowski @ 2011-11-04 13:28 UTC (permalink / raw) To: 'Jonghun Han', linux-media; +Cc: 'Hans Verkuil' Hello, On Friday, November 04, 2011 2:08 PM Jonghun Han wrote: > I'm not sure the meaning of variables in v4l2_pix_format and v4l2_plane. > Especially bytesperline, sizeimage, length and bytesused. > > v4l2_pix_format.width = width > v4l2_pix_format.height = height > v4l2_pix_format.bytesperline = bytesperline [in bytes] > v4l2_pix_format.sizeimage = bytesperline * buf height -> Is this > right ? Yes, I would expect it to be calculated this way for formats where bytesperline can be defined (for macroblock format bytesperline is hard to define). > > v4l2_plane.length = bytesperline * buf height -> Is this right ? > I don't which is right. > v4l2_plane.bytesused = bytesperline * (top + height) > v4l2_plane.bytesused = bytesperline * height > v4l2_plane.bytesused = width * height * bytesperpixel > v4l2_plane.bytesused = bytesperline * (top + height) - (pixelperline - > (left + width)) * bytesperpixel bytesused should indicate how many bytes have been modified from the beginning of the buffer, so memcpy(dst, buf->mem, byteused) will copy all the video data. So probably the most appropriate value for bytesused is: v4l2_plane.bytesused = bytesperline * (top + height) I hope my assumptions are correct, but I would also like Hans to comment on this. > I assumed the following buffer. > > | | > |<--------------------- bytesperline --------------------->| > | | > +----------------------------------------------------------+----- > | ^ | ^ > | | | | > | | | > | t | | > | o | | > | p | | > | | | > | | | | > | V |<--------- width ---------->| | | > |<-- left -->+----------------------------+ - | | > | | | ^ | > | | | | | b > | | | | | u > | | | | f > | | | h | > | | | e | h > | | | i | e > | | | g | i > | | | h | g > | | | t | h > | | | | t > | | | | | > | | | | | | > | | | v | | > | +----------------------------+ - | | > | | | > | | | > | | v > +----------------------------------------------------------+----- Best regards -- Marek Szyprowski Samsung Poland R&D Center ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Query the meaning of variable in v4l2_pix_format and v4l2_plane 2011-11-04 13:28 ` Marek Szyprowski @ 2011-11-04 14:48 ` Hans Verkuil 0 siblings, 0 replies; 4+ messages in thread From: Hans Verkuil @ 2011-11-04 14:48 UTC (permalink / raw) To: 'Jonghun Han' Cc: Marek Szyprowski, linux-media, 'Hans Verkuil' On Friday 04 November 2011 14:28:48 Marek Szyprowski wrote: > Hello, > > On Friday, November 04, 2011 2:08 PM Jonghun Han wrote: > > I'm not sure the meaning of variables in v4l2_pix_format and v4l2_plane. > > Especially bytesperline, sizeimage, length and bytesused. > > > > v4l2_pix_format.width = width > > v4l2_pix_format.height = height buf_height, actually (based on your picture). > > v4l2_pix_format.bytesperline = bytesperline [in bytes] > > v4l2_pix_format.sizeimage = bytesperline * buf height -> Is this > > right ? > > Yes, I would expect it to be calculated this way for formats where > bytesperline can be defined (for macroblock format bytesperline is hard > to define). Correct. For formats where bytesperline is meaningless I guess most drivers will leave this at 0. It's not actually specced what it should be in those cases. > > v4l2_plane.length = bytesperline * buf height -> Is this right ? > > I don't which is right. > > v4l2_plane.bytesused = bytesperline * (top + height) > > v4l2_plane.bytesused = bytesperline * height > > v4l2_plane.bytesused = width * height * bytesperpixel > > v4l2_plane.bytesused = bytesperline * (top + height) - (pixelperline - > > (left + width)) * bytesperpixel > > bytesused should indicate how many bytes have been modified from the > beginning of the buffer, so memcpy(dst, buf->mem, byteused) will copy > all the video data. > > So probably the most appropriate value for bytesused is: > v4l2_plane.bytesused = bytesperline * (top + height) The bytesused field is set by the driver when you capture video and will typically be equal to bytesperline * buf_height. For compressed formats it can be any value <= sizeimage though. For video output it is the application that fills in bytesused. However, I want to add something here: it is currently not possible to specify anything other than horizontal padding. I.e., bytesperline can be more than the width, allowing for a right margin, but you can't specify a left margin. So left == 0 at the moment. Also, in the current API top == 0 as well. Drivers can set the data_offset field in v4l2_plane to a non-zero value, and that might be a way to create a top margin, but this is really meant for meta data that is carried at the beginning of a buffer. Recent discussions led to a proposal to add a app_offset field where applications can specify an additional offset from the beginning of the buffer. But this has not been added. Regards, Hans > I hope my assumptions are correct, but I would also like Hans to comment > on this. > > > I assumed the following buffer. > > > > |<--------------------- bytesperline --------------------->| > > > > +----------------------------------------------------------+----- > > > > | ^ | ^ > > | > > | > > | t | | > > | o | | > > | p | | > > | > > | > > | V |<--------- width ---------->| | | > > | > > |<-- left -->+----------------------------+ - | | > > | > > | | | ^ | > > | | | > > | | | | | b > > | | | | | u > > | | | | | > > | | | | f > > | | | > > | | | h | > > | | | e | h > > | | | i | e > > | | | g | i > > | | | h | g > > | | | t | h > > | | | > > | | | | t > > | | | > > | | | v | | > > | > > | +----------------------------+ - | | > > | > > | | v > > > > +----------------------------------------------------------+----- > > Best regards ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Query the meaning of variable in v4l2_pix_format and v4l2_plane 2011-11-04 13:07 Query the meaning of variable in v4l2_pix_format and v4l2_plane Jonghun Han 2011-11-04 13:28 ` Marek Szyprowski @ 2011-11-04 16:02 ` Tomasz Stanislawski 1 sibling, 0 replies; 4+ messages in thread From: Tomasz Stanislawski @ 2011-11-04 16:02 UTC (permalink / raw) To: Jonghun Han; +Cc: linux-media, m.szyprowski On 11/04/2011 02:07 PM, Jonghun Han wrote: > > Hi, Hi Mr. Han, > > I'm not sure the meaning of variables in v4l2_pix_format and v4l2_plane. > Especially bytesperline, sizeimage, length and bytesused. > > v4l2_pix_format.width = width > v4l2_pix_format.height = height The fields width and height are undefined for some formats, like compressed JPEG and video streams. > v4l2_pix_format.bytesperline = bytesperline [in bytes] The spec says "Distance in bytes between the leftmost pixels in two adjacent lines" for the largest plane. For YUV 4:2:0 the largest plane is luminance, where one pixel is one byte. > v4l2_pix_format.sizeimage = bytesperline * buf height -> Is this > right ? It is the upper limit for size of image of desired size. This value is needed if images are passed in compressed formats. > > v4l2_plane.length = bytesperline * buf height -> Is this right ? > I don't which is right. This is the upper limit for a size of a given plane. For simple formats use: v4l2_plane.length = plane_height * plane.bytesperline The plane_height may be smaller the buf_height. For example for YUV420, the height of the chrominance plane, should be the half of buf_height. For compressed formats it specify upper limit for plane size. > v4l2_plane.bytesused = bytesperline * (top + height) > v4l2_plane.bytesused = bytesperline * height > v4l2_plane.bytesused = width * height * bytesperpixel > v4l2_plane.bytesused = bytesperline * (top + height) - (pixelperline - > (left + width)) * bytesperpixel bytesused specify how much valid data is present in the buffer. For simple formates you should use: v4l2_plane.bytesused = v4l2_plane.length while queuing buffer into OUTPUT queue. The inner rectangle refers to cropping rectangle for mem2mem devices. This rectangle should not be used in any computations of the buffer parameters. Best regards, Tomasz Stanislawski > > I assumed the following buffer. > > | | > |<--------------------- bytesperline --------------------->| > | | > +----------------------------------------------------------+----- > | ^ | ^ > | | | | > | | | > | t | | > | o | | > | p | | > | | | > | | | | > | V |<--------- width ---------->| | | > |<-- left -->+----------------------------+ - | | > | | | ^ | > | | | | | b > | | | | | u > | | | | f > | | | h | > | | | e | h > | | | i | e > | | | g | i > | | | h | g > | | | t | h > | | | | t > | | | | | > | | | | | | > | | | v | | > | +----------------------------+ - | | > | | | > | | | > | | v > +----------------------------------------------------------+----- > > > Best regards, > > ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2011-11-04 16:03 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2011-11-04 13:07 Query the meaning of variable in v4l2_pix_format and v4l2_plane Jonghun Han 2011-11-04 13:28 ` Marek Szyprowski 2011-11-04 14:48 ` Hans Verkuil 2011-11-04 16:02 ` Tomasz Stanislawski
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