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Problem was detected while investigating the crash when running GStreamer pipeline with vaapisink over SSH with X Forwarding.

VA_API version 1.8.0 LibVA 2.8.0

in va_x11.c

234 static VAStatus va_DisplayContextGetNumCandidates ( 
235     VADisplayContextP pDisplayContext,
236     int *num_candidates
237 )
238 {
239     VAStatus vaStatus;
240 
241     vaStatus = va_DRI2_GetNumCandidates(pDisplayContext, num_candidates);
242 
243     /* A call to va_DisplayContextGetDriverName will fallback to other
244      * methods (i.e. NVCTRL, FGLRX) when DRI2 is unsuccessful.  All of those
245      * fallbacks only have 1 candidate driver.
246      */
247     if (vaStatus != VA_STATUS_SUCCESS)
248       *num_candidates = 1;
249 
250     return VA_STATUS_SUCCESS;
251 }

va_DisplayContextGetNumCandidates always returns SUCCESS status even if the DRI2 is not authed. Seems like return status is not correct for this case.

SSH with X Forwarding is not a local X, but the dri2 protocol only supports local rendering. The problem is, this check always succeeds even dri2 auth fails. The gstreamer as a middle level sw, just go on because no error reported and considers the init succeeds. Later, when it really call dri2's render functions, it will crash there.