[maemo-developers] raw image buffer and gstv4l2camsrc

[From: Nicolai Hess]

Hi,
I hope someone can help me or points me to someone else how knows
something about the gstv4l2camsrc.

I have got a question regarding raw-image buffers in gstv4l2camsrc.c
(in gstreamer0.10-plugins-camera-
0.79 for Fremantle).

I am interested in this method:
gst_v4l2camsrc_send_raw_frame (GstV4l2CamSrc *v4l2camsrc, GstBuffer *buf).
I know the method can copy the raw-image buffer end send this over the
GstBus.
This would be a good way to make raw-images with the N900 camera.

But sadly not the full image data is copied. Here are my observations:

The cameradriver somewhere decides(I couldn't find out where or how) the
biggest
image resolution would be 2576x1960 pixels with 2 bytes per pixel, so the
image data would
be  10097920 bytes.
In the method:
gst_v4l2camsrc_send_raw_frame (GstV4l2CamSrc *v4l2camsrc, GstBuffer *buf)
are two GstBuffer,
the argument of this method "buf" which holds the image data from the camera
driver
and the new copy of this buffer "raw_buffer".

buf buffer is copied with:
  raw_buffer = gst_buffer_copy (buf);

The amount of bytes copied are based on the size of the source buffer
(10097920 bytes).
Now the raw_buffer size attribute is changed based on the raw_caps from the
camera driver:
  /* calculate raw_size from raw_caps */
  raw_s = gst_caps_get_structure (raw_caps, 0);
  gst_structure_get_int (raw_s, "width", &raw_width);
  gst_structure_get_int (raw_s, "height", &raw_height);
  raw_size = raw_width * raw_height * 2;

But the raw_buffer size isn't 10097920, the actual size is computed based
on the bayer-raw BA10 format with a 2952x1968 resolution with 2 bytes per
pixel.

That means the buffer copy send over GstBus has the size 10202112, but the
last
104192 are mostly garbage because the call
  raw_buffer = gst_buffer_copy (buf);
only wrote bytes of "buf" data (10097920).

Of course, I could change my application to store only a raw-image of
2576x1960.
But what bothers me is, the source buffer (buf) actually has the full
2592x1968x2 data!
I made a quick and dirty change to the above mentioned method to write out
the
full buffer, and it indeed contains valid image data.

So, my questions are, is it a bug, that the source buffer thinks its size is
10097920,
whereas it actually holds 10202112 bytes of image data?
And where is this 2576x1960 resolution setting? When I request the supported
resolutions (v4l2camsrc->formats) I don't get 2576x1960 but 2592x1968
instead.

regards
Nicolai
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