[Spice-devel] GStreamer's zero-copy code is broken

[Frediano Ziglio]

> 
> The patch below breaks the zero-copy code in the GStreamer video
> encoder:
> 
> commit c3d237075b994fe67edddd58f2b3164cb579e6f4
> Author: Frediano Ziglio <fziglio at redhat.com>
> Date:   Mon Dec 12 17:22:50 2016 +0000
> 
>     gstreamer: Avoid memory copy if strides are different
>     
>     If bitmap stride and stream stride are different copy was used.
>     Using GStreamer 1.0 you can avoid the copy setting correctly
>     image offset and stride.
>     
>     Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
>     Acked-by: Christophe Fergeau <cfergeau at redhat.com>
> 
> 
> The symptom is that each SpiceBitmap chunk gets incrementally shifted 8
> pixels to the right. See the attached screenshot. Interestingly the 8
> extra pixels don't seem to really be random but they don't seem to be
> identical either.
> 
> Anyway, commenting out the gst_buffer_add_video_meta_full() line fixes
> it (in cases where there is no need for cropping) but of course is
> defeats the purpose of the patch.
> 
> I did not see anything obviously wrong in the patch. The bug is
> unrelated to the codec: it happens with mjpeg, vp8 and h264. So to
> reproduce it simply make sure you're using GStreamer for video, grab
> big_buck_bunny_480p_h264.mov and play it with either mplayer or totem.
> 
> Maybe it's a gstreamer bug? Here I'm using 1.10.2.
> 
> --
> Francois Gouget <fgouget at codeweavers.com>

Manage to reproduce with my tests. just use the --split-lines options.
Seems I forgot why I added this option!

Frediano