Geoffrey Hausheer wrote:
You'd need to recompile with debug enabled, and might need a
thread-capable gdb. make sure to always use 'thread apply all bt'
when debugging. But this looks like a failure inside of libavcodec,
which makes little sense. My guess is that the problem is happening
in build_frame.
With debug enabled it faults in the avcodec_encode_video() function
(specifically in the dct_quantize_SSE2 method). Here's a backtrace from
the thread:
(gdb) bt
#0 0xb740f246 in dct_quantize_SSE2 (s=0xb71e7783, block=0x8229450,
n=135775936, qscale=0, overflow=0x2) at mpegvideo_mmx_template.c:152
#1 0x08229450 in ?? ()
#2 0xb71e7783 in encode_mb (s=0x8229450, motion_x=0, motion_y=0)
at mpegvideo.c:4243
#3 0xb71ecb9d in encode_thread (c=0x84555f0, arg=0x8229450)
at mpegvideo.c:5146
#4 0xb71ceaa4 in avcodec_default_execute (c=0x84555f0,
func=0xb71ea590 <encode_thread>, arg=0x8229514, ret=0x0, count=1)
at utils.c:420
#5 0xb71de764 in MPV_encode_picture (avctx=0x84555f0, buf=0xb5d9d008 "",
buf_size=-128, data=0x8140f60) at mpegvideo.c:5457
#6 0xb71d022a in avcodec_encode_video (avctx=0x84555f0,
buf=0xffffff80 <Address 0xffffff80 out of bounds>, buf_size=614400,
pict=0x8140f60) at utils.c:868
#7 0x0804c838 in MPEG2fixup::build_frame (this=0xbfa71084, pkt=0xbfa70c2c,
fname=0x0) at mpeg2fix.cpp:929
#8 0x0804ce67 in MPEG2fixup::convert_to_i (this=0xbfa71084, frameNum=0,
numFrames=2, headPos=0) at mpeg2fix.cpp:1194
#9 0x08050699 in MPEG2fixup::start (this=0xbfa71084) at mpeg2fix.cpp:1458
#10 0x08051a89 in main (argc=7, argv=0xbfa72404) at mpeg2fix.cpp:1775
It is interesting to not that the buf paramter to avcodec_encode_video()
is bad in the bt, but was valid when it was passed. Since it appears to
be an alignment issue, I changed the passed Context to disable all
MMX/SSE routines. I got this output, no segfaults, and a working mpg
file it seems:
Opening /mnt/store/1015_20051108183000.mpg
[mpeg2video @ 0xb7454f04]libavcodec: CPU flags: mmx mmxext sse sse2
Input #0, mpeg, from '/mnt/store/1015_20051108183000.mpg':
Duration: N/A, bitrate: N/A
Stream #0.0[0x1e0], 29.97 fps: Video: mpeg2video, yuv420p, 640x480,
6000 kb/s
Stream #0.1[0x1c0]: Audio: mp2, 48000 Hz, stereo, 384 kb/s
#0 PTS:36039 Delta: 0.000000ms queue: 11
#1 PTS:34685 Delta: 15.044444ms queue: 2
Mux rate: 6.49 Mbit/s
[mpeg2video @ 0xb7454f04]libavcodec: CPU flags:
Warning, QMAT_SHIFT is larger then 21, overflows possible
Converting frame 0 to an I-frame ((null))
[mpeg2video @ 0xb7454f04]libavcodec: CPU flags:
Warning, QMAT_SHIFT is larger then 21, overflows possible
Converting frame 1 to an I-frame ((null))
[mpeg2video @ 0xb7454f04]libavcodec: CPU flags:
Warning, QMAT_SHIFT is larger then 21, overflows possible
Converting frame 9 to an I-frame ((null))
[mpeg2video @ 0xb7454f04]libavcodec: CPU flags:
Warning, QMAT_SHIFT is larger then 21, overflows possible
Converting frame 10 to an I-frame ((null))
[mpeg2video @ 0xb7454f04]libavcodec: CPU flags:
Warning, QMAT_SHIFT is larger then 21, overflows possible
Converting frame 11 to an I-frame ((null))
Just be awate, this tool is still in the debugging stage. You
certainly won't want to replace the orginal files with processed ones
at this point. As soon as I am convinced the code is working pretty
well, it will be added to myth, at which times such scripts won't be
needed.
Yeah the shell script is just nice to have so I don't have to figure
out what the cutpoints are for every file I want to test with.
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