theoraenc can't be initialized

[Arvin6]

I'm running a pipeline that streams OpenGL framebuffer from my osx app using
appsrc. 

appsrc ! videoconvert ! theoraenc ! oggmux ! tcpserversink port=8554"

It worked well with
gst_parse_launch( " videotestsrc ! videoconvert ! theoraenc ! oggmux !
tcpserversink port=8554", NULL)

I'm just changing the source to appsrc here.

Error from bus:
ERROR from element encoding: Erreur GStreamer?: probl?me de n?gociation.

Debugging info: gstvideoencoder.c(1449): GstFlowReturn
gst_video_encoder_chain(GstPad *, GstObject *, GstBuffer *) ():
/GstPipeline:phostechpipe/GstTheoraEnc:encoding:
encoder not initialized



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