[gst-devel] Segfault when using callbacks in gst-python for buffer retrieval

[Matthias Blaicher]

Hallo together,

I'm working on a project which requires me to to buffer frames from a
video4linux source in Python. I decided that gstreamer is perfectly
fit for such a task and have already tried some initial code - Which
all fail in a non spectacular segfault.

Here is what I'm trying to do:

I have such a path:
v4lsrc ! video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace !
pngenc snapshot=False  ! fakesink name=sink

Which should generate a continuous stream of png frames. Now i try to
intercept the exchanged Buffer objects by using the handoff event of
fakesink with a callback.  But whenever I activate the callback, the
python interpreter dies with a segmentation fault.  I also tried to
intercept the Buffers with the Pad.add_buffer_probe call, but that
fails the same way.

My code is:

import gst
import time

gst.debug_set_active(True)
gst.debug_set_default_threshold(4)


def callback(fakesink, buffer, pad, data=None):
   return True


def probe_callback_fakesrc(pad, buffer):
   return True

#v4lsrc
pipeline = gst.parse_launch('videotestsrc !
video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace ! pngenc
snapshot=False  ! fakesink name=sink')
fakesink = pipeline.get_by_name('sink')

# Way 1
fakesink.props.signal_handoffs = True
fakesink.connect("handoff", callback)

## Way 2
#pad = fakesink.get_pad('sink')
#pad.add_buffer_probe(probe_callback_fakesrc)

pipeline.set_state(gst.STATE_PLAYING)

while True:
   #Sleep so that context switching for gst works
   time.sleep(1)



Which fails such as (with debug leve 4 and strace)

0:00:04.553704144  9029 0x832f1d8 INFO            GST_STATES
gstelement.c:2148:gst_element_continue_state:<sink> completed state
change to PLAYING
0:00:04.553717205  9029 0x832f1d8 INFO            GST_STATES
gstelement.c:2161:gst_element_continue_state:<sink> posting
state-changed PAUSED to PLAYING
0:00:04.553714760  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1508:gst_base_sink_wait_preroll:<sink> continue after
preroll
0:00:04.553743117  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1678:gst_base_sink_do_sync:<sink> possibly waiting for
clock to reach 0:00:00.000000000
0:00:04.553763652  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1468:gst_base_sink_wait_clock:<sink> sync disabled
0:00:04.553784466  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1684:gst_base_sink_do_sync:<sink> clock returned 4
0:00:04.553798993  9029 0x8325750 DEBUG             basesink
gstbasesink.c:2029:gst_base_sink_render_object:<sink> rendering buffer
0x8328e68
0:00:04.553789634  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:337:gst_bus_post:<bus0> [msg 0x83321d0] posting on bus, type
state-changed, GstMessageState, old-state=(GstState)GST_STATE_PAUSED,
new-state=(GstState)GST_STATE_PLAYING,
pending-state=(GstState)GST_STATE_VOID_PENDING; from source <sink>
0:00:04.553835034  9029 0x832f1d8 DEBUG                  bin
gstbin.c:2719:gst_bin_handle_message_func:<pipeline0> [msg 0x83321d0]
handling child sink message of type state-changed
0:00:04.553848933  9029 0x832f1d8 DEBUG                  bin
gstbin.c:2923:gst_bin_handle_message_func:<pipeline0> posting message
upward
0:00:04.553862133  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:337:gst_bus_post:<bus1> [msg 0x83321d0] posting on bus, type
state-changed, GstMessageState, old-state=(GstState)GST_STATE_PAUSED,
new-state=(GstState)GST_STATE_PLAYING,
pending-state=(GstState)GST_STATE_VOID_PENDING; from source <sink>
0:00:04.553889303  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:367:gst_bus_post:<bus1> [msg 0x83321d0] pushing on async
queue
0:00:04.553887906  9029 0x8325750 DEBUG                pygst
pygstminiobject.c:152:pygstminiobject_new: have to create wrapper for
object 0x8328e68
0:00:04.553904041  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:372:gst_bus_post:<bus1> [msg 0x83321d0] pushed on async queue
0:00:04.553913679  9029 0x8325750 DEBUG                pygst
pygstminiobject.c:171:pygstminiobject_new: created Python object
0xb7ddc800 for GstMiniObject 0x8328e68 [ref:4]
0:00:04.553917870  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:363:gst_bus_post:<bus0> [msg 0x83321d0] dropped
0:00:04.553937357  9029 0x832f1d8 DEBUG           GST_STATES
gstelement.c:2380:gst_element_set_state_func:<sink> returned SUCCESS
)     = ? ERESTARTNOHAND (To be restarted)
+++ killed by SIGSEGV +++
Process 9029 detached

I use Ubuntu Hardy with gst.version() == (0, 10, 18, 0)

Does  anybody know what I'm doing wrong here?

Sincerely,

Matthias Blaicher