On Fri, 24 Feb 2017, Francois Gouget wrote:
> On Fri, 24 Feb 2017, Christophe de Dinechin wrote:
> [...]
> > Looking at the patch, I wonder why we pass an offset and a stride from
> > different sources (offset is from the source, but stride is from the
> > bitmap)? Shouldnʼt we use the stream stride?
>
> I think that's correct:
> * bitmap->{x,y} are the width and height of the source image.
>
> * bitmap->stride is the size in bytes of each line. In other words
> that's how much you must add to the pointer to get the pixel of the
> next line.
>
> * src->{left,right,top,bottom} identifies which subset of the source
> image should be encoded and sent to the client. So the offset
> corresponds to the src->left.
>
> However I don't see any way to tell gst_buffer_add_video_meta_full()
> that you only want to take 400 pixels out of every 640 pixel line, or
> only 200 lines out of the 480 lines.
>
> For instance if we have
> bitmap->x = 640
> bitmap->y = 480
> bitmap->stride = 2560
> src->left = src->top = 0
> src->right = 200
> src->bottom = 100
>
> Then we will call:
>
> gst_buffer_add_video_meta_full(buffer, GST_VIDEO_FRAME_FLAG_NONE,
> encoder->format->gst_format,
> 640 /* bitmap->x */, 480 /* bitmap->y */,
> 1,
> { 0 } /* offset */,
> { 2560 } /* stride */);
>
> How will GStreamer know that it should encode a 200x100 video since we
> did not tell it that:
> src->right - src->left = 200
> src>bottom - src->top = 100
Actually the GStreamer pipeline 'knows' the size of the area to encode
through the source caps which are then (if I remember correctly)
attached to the buffer.
Also src->top is taken into account through the chunk_offset value which
is the offset in bytes into the bitmap data computed by zero_copy().
--
Francois Gouget <fgouget@xxxxxxxxxxxxxxx>_______________________________________________
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