hi Michael,
On Wed, 2002-10-16 at 16:40, Michael H. Schimek wrote:
> Sequential is always oldest first (fields stored in transmitted =
> temporal order). The app asks for any of V4L2_FIELD_SEQ_TB or
> V4L2_FIELD_SEQ_BT and the driver returns whatever applies.
Exactly.
> Likewise alternating fields are passed in transmitted = temporal order,
> starting with what? One could check V4L2_BUF_FLAG_TOPFIELD/BOTFIELD, but
> it seems they're gone.
enum v4l2_field {
[..]
V4L2_FIELD_TOP = 2, /* top field only */
V4L2_FIELD_BOTTOM = 3, /* bottom field only */
[..]
};
Isn't that what you're looking for?
> I assumed cropping dimensions apply to capture & overlay alike. A type
> field allows two sets of cropping parameters in simultaneous
> capture/overlay mode. Do you want that?
Yes. For JPEG capture, for example, you can set cropping information,
while the overlay is still uncropped.
> > struct v4l2_jpegcompression
> > {
> > int quality;
> >
> > int APPn; /* Number of APP segment to be written,
> > * must be 0..15 */
> > int APP_len; /* Length of data in JPEG APPn segment */
> > char APP_data[60]; /* Data in the JPEG APPn segment. */
> >
> > int COM_len; /* Length of data in JPEG COM segment */
> > char COM_data[60]; /* Data in JPEG COM segment */
> >
> > __u32 jpeg_markers; /* Which markers should go into the JPEG
> > * output. Unless you exactly know what
> > * you do, leave them untouched.
> > * Inluding less markers will make the
> > * resulting code smaller, but there will
> > * be fewer aplications which can read it.
> > * The presence of the APP and COM marker
> > * is influenced by APP_len and COM_len
> > * ONLY, not by this property! */
> >
> > #define V4L2_JPEG_MARKER_DHT (1<<3) /* Define Huffman Tables */
> > #define V4L2_JPEG_MARKER_DQT (1<<4) /* Define Quantization Tables */
> > #define V4L2_JPEG_MARKER_DRI (1<<5) /* Define Restart Interval */
> > #define V4L2_JPEG_MARKER_COM (1<<6) /* Comment segment */
> > #define V4L2_JPEG_MARKER_APP (1<<7) /* App segment, driver will
> > * allways use APP0 */
> > };
>
> Someone please explain this, better yet write the spec. IMHO it's
> pointless to add when we don't know how this works, what the purpose is.
I'm sorry, here's some short explanation:
APP is some application-specific information. The application can set it
itself, and it'll be stored in the JPEG-encoded fields (e.g. interlacing
information for in an AVI or so). COM is the same, but it's comments,
like 'encoded by me' or so.
jpeg_markers describes whether the huffman tables, quantization tables
and the restart interval information (all JPEG-specific stuff) should be
stored in the JPEG-encoded fields. These define how the JPEG field is
encoded. If you omit them, applications assume you've used standard
encoding. You usually do want to add them.
I hope this is clear.
Ronald
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