Renegotiate GstVaapiDecode src caps

Víctor Jáquez vjaquez at
Tue Nov 21 17:19:29 UTC 2017

On Tue, 21 Nov 2017 at 13:46, Danny Cullen wrote:
> Hello,
> I am using a GstURIDecodeBin to access an HTTP MJPEG IP video source.  The
> source sends the first few frames as 800x600 (a black splash screen) JPEG
> images and then sends the live data as 352x288.
> When the first frame is decoded I link a GstVaapiPostproc element with the
> GstURIDecodeBin and the vaapipostproc sink caps are negotiated with the
> vaapidecode elements src caps as 800x600.
> When the JPEG images change size, the sink caps of the vaapidecode element
> receive a GST_EVENT but this does not propagate to any of the downstream
> elements.
> I’m assuming that the sink of the vaapipostproc element would need to
> renegotiate with the src of the vaapidecode element?  Is that correct?

It is tricky since vaapipostproc resize the frame, thus there's no need to
renegotiate because resizing is assumed.

> I have connected a notify::caps signal handler to the sink pad of the
> vaapidecode element however I’m not sure of the best way of getting the
> downstream elements to renegotiate.  What is the best way of achieving this?

I guess that's is a way to workaround this in your case.

> Thanks in advance,
> Danny
> Danny Cullen
> Software Team Leader
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