HELP: RGB buffer format query (I am trying to pass a buffer to appsrc)

[Edward Anon]

Before figuring out how to make an appsrc take an OpenGL texture, I wanted
to pass an RGB buffer.  I played with this
<https://gist.github.com/floe/e35100f091315b86a5bf#file-gst-appsrc-c-L14>
example for a while and ended up with this code
<https://pastebin.com/A0vnK5LB>.

Like the example, I can happily get the screen to alternate between white
and black. However, I don't understand the structure of the buffer
GStreamer expects.

Why does GStreamer seem to expect the minimum buffer size to be WIDTH *
HEIGHT * CHANNELS + HEIGHT? Why is it not just WIDTH * HEIGHT * CHANNELS
for an RGB buffer (where the array passed as the buffer is an array of
bytes)? Why would I want to pass a larger buffer?

Also, when I try to set the colour to green, red or blue and only write to
the first WIDTH * CHANNELS bytes in the buffer I get one clean row of the
expected colour. However, this row changes colour when I write to the next
WIDTH * CHANNELS bytes. Why is this? How do I fix it?

I suspect the queries are related. Thanks in advance.
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