When using the following pipelines for sending/receiving an jpeg encoded videostream using videotestsrc and udpsink, the receiver cancels with the following error message:

 When starting above pipelines or this sample application you will encounter
 the following error on receiving end:

   ** (gst-launch-1.0:32310): CRITICAL **: gst_adapter_push: assertion `GST_IS_BUFFER (buf)' failed
   ** (gst-launch-1.0:32310): CRITICAL **: gst_jpeg_dec_fill_input_buffer: assertion `dec->current_frame_map.data != NULL' failed
   ** (gst-launch-1.0:32310): CRITICAL **: gst_jpeg_dec_fill_input_buffer: assertion `dec->current_frame_map.data != NULL' failed
   ERROR: From element /GstPipeline:pipeline0/GstJpegDec:jpegdec0: Failed to decode JPEG image
   Additional diagnostic information:
   gstjpegdec.c(1295): gst_jpeg_dec_handle_frame (): /GstPipeline:pipeline0/GstJpegDec:jpegdec0:
   number of components not supported: 3 (max 3)

Use these pipelines for reproduction:

RECEIVER: 
 gst-launch-1.0 -v udpsrc port=9001 ! "application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)JPEG, payload=(int)96" ! rtpjpegdepay ! jpegdec ! autovideosink

SENDER: 
 gst-launch-1.0 -v videotestsrc pattern=1 ! "video/x-raw, width=(int)640, height=(int)480, framerate=(fraction)30/1, format=(string)I420" ! jpegenc ! rtpjpegpay ! udpsink host=127.0.0.1 port=9001

The problem was encountered using GStreamer 1.0.8 and verified also with GStreamer 1.0.9. It will only occur with pattern=1 of videotestsrc and with 640x480 resolution. When using pattern=0 and resolution 320x240 I could not see the error. When using avenc_mjpeg instead of jpegenc the problem also seems to be fixed. Therefore I guess its a problem of jpegenc.