Dynamic pipeline (videosink swapping)

[Rob Kramer]

On 4/4/22 15:48, Victor Jaquez via gstreamer-devel wrote:
>
>> Thanks again, that seems to select the vampeg2dec element, and seems to work
>> with my dynamic sink plugger example..
>>
>> In the dot file, there is no mention of VASurface anymore though. Is that
>> expected, or are things being copied between video and main memory? When
>> using gst-play-1.0, it does look like the vampeg2dec version uses ~5% less
>> CPU (~10% vs ~15%).
> Yes, when the va decoder negotiates with downstream, it tries to check
> if downstream can handle video meta, if it doesn't (which tee might
> report drop), va encoder internally downloads and copies the frame onto
> system memory.
>
>> I've uploaded a dot-file from gst-play, in case you'd like to have a look:
>> https://pastebin.com/VYPXJP2d
> Even more, your pipeline does a color conversion in CPU memory.

No tee was involved here, these were just gst-play tests.

I thought maybe the va decoder can't negotiate to a VASurface because I 
had disabled the legacy vaapi support and no vaapisink was available. So 
I reconfigured (and threw away build dir to avoid issues) to include 
gst-vaapi as well.

When I run gst-play (with or without GST_PLUGIN_FEATURE_RANK), this 
doesn't work at all:

   [laprob] ~/gstreamer> gst-play-1.0 /var/sol/media/video/ATC.mpg
   Press 'k' to see a list of keyboard shortcuts.
   Now playing /var/sol/media/video/ATC.mpg
   Redistribute latency...

   (gst-play-1.0:193197): GStreamer-Base-CRITICAL **: 18:20:02.880: 
basetransform: second attempt to fixate caps returned invalid (NULL) 
caps on pad vaapipostproc0:sink

   -snip 5 more-

   ERROR Internal data stream error. for file:///var/sol/media/video/ATC.mpg
   ERROR debug information: 
../../gstreamer/subprojects/gst-plugins-bad/gst/mpegdemux/gstmpegdemux.c(3080): 
gst_ps_demux_loop (): 
/GstPlayBin:playbin/GstURIDecodeBin:uridecodebin0/GstDecodeBin:decodebin0/GstMpegPSDemux:mpegpsdemux0:
   streaming stopped, reason not-negotiated (-4)
   Reached end of play list.

When I explicitly request a vaapisink, it works as expected (without 
GST_PLUGIN_FEATURE_RANK), and uses VASurfaces everywhere:

   GST_DEBUG_DUMP_DOT_DIR=. gst-play-1.0 --videosink=vaapisink 
/var/sol/media/video/ATC.mpg

The same command with GST_PLUGIN_FEATURE_RANK set works fine too, but 
doesn't use the new vampeg2dec module anywhere. Are these two VA plugins 
able to interoperate, or am I misunderstanding something? I was going to 
upload a level 5 debug output to pastebin, but my browser explodes if I 
try paste it..

I don't need gst-play btw, but it's nice to test core functionality that 
way, so that I can rule out errors on my side.

Cheers,

     Rob