NV12 issue in 1.14.1

[tobatrance]

Hi there,

I'm right now shifting my application from 1.8.3 to 1.14.1 as I shift Ubuntu
as well from 16.04 to 18.04. I got some issues with the NV12 format. Back in
1.8.3 almost all my videos came in I420, meanwhile they're by default
encoded in NV12. 

I'm in general using this simple pipeline:

filesrc ! decodebin ! appsink

I grab the frames from my appsink and push them on to OpenGL for some
postprocessing before displaying them. There are *some* videos which cause
trouble, the majority runs fine, like bunny e.g., but some don't work the
way they're supposed to which have been working with I420. Said that I can
exclude my shader being wrong. Please note the attached video. This is one
of these working before in I420 but not in NV12. 

countdown.mp4
<http://gstreamer-devel.966125.n4.nabble.com/file/t377636/countdown.mp4>  

To me it seems that the strides given by the GstVideoInfo.stride property do
not fit the corresponding GstVideoFrame.data property. For the countdown
video, when using the stride 765 in 1.14.1/NV12 for the Y plane it works
properly. In 1.8.3/I420, GST gives 720, which is the same as the actual
width and it works there. In 1.14.1/NV12 it also gives 720 but as I
mentioned it's not displayed correctly. When changing the value to 765 it
works. I'm using the stride in /glPixelStorei(GL_UNPACK_ROW_LENGTH,
stride);/ when updating the texture with the current sample's buffer.

I got a different issue with the UV plane: The strides there don't work as
well like with the Y plane. But additionally it seems that the plane has an
offset in respect to the Y plane. When swichting off displaying the Y plane
in the shader and just showing the UV plane it seems the UV plane is shifted
to the top. In other words: It seems like the first couple of rows are
missing in the UV plane. The bottom is filled with visual noise. 

Appreciate any help. If you need more information let me know.



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