[XviD-devel] crash in get_intra_block()

[Rob Prowel]

hi.

I am designing a wirelessly operated system that uses
low bitrate 352x240 MPEG4 to tele-operate an unmanned
vehicle.  My system MUST use 4096 byte fragmented UDP
to communicate with the robot.  I add some header
information and reassemble the complete frame upon
receipt.  I set 30fps and key frames inserted every
16th frame, with no B frames.  I am using a PC104
MPEG4 hardware encoder that I know generates bad
macroblocks on occasion: IME6400 firmware error that
the vendor won't fix.  Of course my embedded OS is
Linux 2.6.17.  Anyway, fixing the firmware is not an
option.  Also, I must consider that because of UDP
tranport some of the packets may arrive with pieces
missing or not at all.

I analyzed a core dump of my operator console
application and noted that the get_intra_blocks()
method occasionally causes a segfault.

Anyone care to enlighten me as to how I might fix
this?  It is possible and probable that I could send
the decoder occasional bad frame data and it is
extremely important that the decoder consume the
correct number of input stream bytes and not crash. 
One characteristic of my use case is that I dont
typically send a true bitstream to the decoder, but
only a discrete frames worth of data, with the
exception being that each key frame is always
preceeded by a 27 byte VOL header frame.  The hardware
encoder does it that way.

I noted some DEBUG macros in the get_intra_blocks()
method so I'm guessing someone might be familiar with
why my problem exists.

Any help will be appreciated.

-Rob Prowel


I told my pap and mam I was coming to the mountains to trap and be a mountain man. Acted like they was gut-shot. Says, "son, make your life go here. Here's where the peoples is. Them mountains is for animals and savages." I said, "Mother Gue, the Rocky Mountains is the marrow of the world." And by God I was right. -- Dell Gue "Jeramiah Johnston, (1972)"


       
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