this pipeline :  sinesrc ! speed ! osssink (or any pipeline involving speed) 
gives me "ERROR: pipeline doesn't want to play." 
 
the interesting part of the debug log: 
DEBUG        GST_CAPS(25485) 
gstelement.c(2750):gst_element_negotiate_pads:<sinesrc0> negotiating pads 
DEBUG        GST_CAPS(25485) 
gstelement.c(2797):gst_element_negotiate_pads:<sinesrc0> perform negotiate for 
sinesrc0:src and speed0:sink 
DEBUG        GST_CAPS(25485) gstpad.c(2535):gst_pad_get_caps: get pad caps of 
sinesrc0:src (0x8066980) 
DEBUG        GST_CAPS(25485) gstpad.c(2557):gst_pad_get_caps: using pad 
template 0x8066510 with caps audio/x-raw-int, endianness=(int)1234, 
signed=(boolean)true, width=(int)16, depth=(int)16, rate=(int)[ 1, 
2147483647 ], channels=(int)1 
DEBUG        GST_CAPS(25485) gstpad.c(2535):gst_pad_get_caps: get pad caps of 
speed0:sink (0x81f3c10) 
DEBUG        GST_CAPS(25485) gstpad.c(2557):gst_pad_get_caps: using pad 
template 0x80a4200 with caps audio/x-raw-int, rate=(int)[ 1, 2147483647 ], 
channels=(int)[ 1, 2147483647 ], endianness=(int){ 1234, 4321 }, width=(int)
{ 8, 16, 32 }, depth=(int)[ 1, 32 ], signed=(boolean){ true, false }; 
audio/x-raw-float, rate=(int)[ 1, 2147483647 ], channels=(int)1, 
endianness=(int)1234, buffer-frames=(int)[ 1, 2147483647 ] 
DEBUG        GST_PADS(25485) gstpad.c(1258):gst_pad_link_negotiate: 
negotiating link from pad sinesrc0:src to pad speed0:sink 
DEBUG        GST_PADS(25485) gstpad.c(1083):gst_pad_link_intersect: 
intersecting link from sinesrc0:src to speed0:sink 
DEBUG        GST_PADS(25485) gstpad.c(1084):gst_pad_link_intersect: ... 
srccaps audio/x-raw-int, endianness=(int)1234, signed=(boolean)true, 
width=(int)16, depth=(int)16, rate=(int)[ 1, 2147483647 ], channels=(int)1 
DEBUG        GST_PADS(25485) gstpad.c(1085):gst_pad_link_intersect: ... 
sinkcaps audio/x-raw-int, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 
2147483647 ], endianness=(int){ 1234, 4321 }, width=(int){ 8, 16, 32 }, 
depth=(int)[ 1, 32 ], signed=(boolean){ true, false }; audio/x-raw-float, 
rate=(int)[ 1, 2147483647 ], channels=(int)1, endianness=(int)1234, 
buffer-frames=(int)[ 1, 2147483647 ] 
DEBUG        GST_PADS(25485) gstpad.c(1086):gst_pad_link_intersect: ... 
filtercaps (NULL) 
DEBUG        GST_PADS(25485) gstpad.c(1098):gst_pad_link_intersect: 
intersection audio/x-raw-int, endianness=(int)1234, signed=(boolean)true, 
width=(int)16, depth=(int)16, rate=(int)[ 1, 2147483647 ], channels=(int)1 
DEBUG        GST_PADS(25485) gstpad.c(1133):gst_pad_link_fixate: trying to 
fixate caps audio/x-raw-int, endianness=(int)1234, signed=(boolean)true, 
width=(int)16, depth=(int)16, rate=(int)[ 1, 2147483647 ], channels=(int)1 
DEBUG        GST_PADS(25485) gstpad.c(1144):gst_pad_link_fixate: app srcpad 
signal fixated to (NULL) 
DEBUG        GST_PADS(25485) gstpad.c(1149):gst_pad_link_fixate: app sinkpad 
signal fixated to (NULL) 
DEBUG        GST_PADS(25485) gstpad.c(1157):gst_pad_link_fixate: srcpad 
sinesrc0:src fixated to audio/x-raw-int, endianness=(int)1234, 
signed=(boolean)true, width=(int)16, depth=(int)16, rate=(int)44100, 
channels=(int)1 
DEBUG        GST_PADS(25485) gstpad.c(1198):gst_pad_link_call_link_functions: 
calling link function on pad sinesrc0:src 
DEBUG         default(25485) gstsinesrc.c(256):gst_sinesrc_link: 
gst_sinesrc_src_link 
DEBUG        GST_PADS(25485) gstpad.c(1214):gst_pad_link_call_link_functions: 
got reply 1 from link function on pad sinesrc0:src 
DEBUG        GST_PADS(25485) gstpad.c(1225):gst_pad_link_call_link_functions: 
calling link function on pad speed0:sink 
DEBUG        GST_PADS(25485) gstpad.c(1242):gst_pad_link_call_link_functions: 
got reply -1 from link function on pad speed0:sink 
INFO         GST_CAPS(25485) gstpad.c(1246):gst_pad_link_call_link_functions: 
pad speed0:sink doesn't accept caps 
INFO       GST_STATES(25485) 
gstelement.c(2714):gst_element_set_state:<sinesrc0> have failed change_state 
return 
INFO       GST_STATES(25485) gstbin.c(751):gst_bin_change_state:<pipeline0> 
child 'sinesrc0' failed to go to state 4(PAUSED) 
DEBUG      GST_STATES(25485) 
gstelement.c(2678):gst_element_set_state:<sinesrc0> element is already in 
requested state READY 
INFO       GST_STATES(25485) 
gstelement.c(2714):gst_element_set_state:<pipeline0> have failed change_state 
return 
ERROR: pipeline doesn't want to play.