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POapplication using ffmpeg segfaults because of for loop?
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  1. POapplication using ffmpeg segfaults because of for loop?
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    copied!<p>I am writing my first ffmpeg application using the tutorial linked to from the ffmpeg.org documentation page [<a href="http://dranger.com/ffmpeg/" rel="nofollow">tutorial</a>] [<a href="https://github.com/mpenkov/ffmpeg-tutorial" rel="nofollow">sample</a>]. Here is my initial code:</p> <pre><code>const char * fnmVideoIn = argv [1]; const char * fnmImageOut = argv [2]; av_register_all (); // [] Open the file AVFormatContext * pcxFormat; if (avformat_open_input (&amp;pcxFormat, fnmVideoIn, NULL, NULL)) { fprintf (stderr, "Could not open file %s for reading\n", fnmVideoIn); return -1; } // [] Get stream information if (avformat_find_stream_info (pcxFormat, NULL) &lt; 0) { fprintf (stderr, "Could not find stream info\n"); return -1; } // [log] print stream info av_dump_format (pcxFormat, 0, fnmVideoIn, 0); </code></pre> <p>and all is well. The program runs without errors and dumps the video info properly. but then I got to the next step...</p> <pre><code>... // [log] print stream info av_dump_format (pcxFormat, 0, fnmVideoIn, 0); int ixVideoStream = -1, ixStrm; for (ixStrm = 0; ixStrm &lt; pcxFormat-&gt;nb_streams; ++ixStrm) { if (pcxFormat-&gt;streams [ixStrm]-&gt;codec-&gt;codec_type == AVMEDIA_TYPE_VIDEO) { ixVideoStream = ixStrm; break; } } </code></pre> <p>and it exits with a segfault. gdb says:</p> <pre><code>(gdb) r test.mp4 out ... Program received signal SIGSEGV, Segmentation fault. 0xb7f572c5 in avformat_open_input () from /usr/lib/libavformat.so.53 </code></pre> <p>how is it possible that <code>avformat_open_input</code> segfaults because of code added <em>after</em> it is called? I even tested it with a regular i=0; i&lt;100 for-loop and it still segfaults! is this a bug? For reference, my system is:</p> <pre><code>$ gcc --version gcc (GCC) 4.7.0 20120414 (prerelease) $ uname -srvmpio Linux 3.3.4-1-ARCH #1 SMP PREEMPT Sat Apr 28 06:04:27 UTC 2012 i686 Intel(R) Core(TM)2 Duo CPU P7450 @ 2.13GHz GenuineIntel GNU/Linux $ ffmpeg -version ffmpeg version 0.10.2 built on Mar 17 2012 08:53:01 with gcc 4.6.3 configuration: --prefix=/usr --enable-libmp3lame --enable-libvorbis --enable-libxvid --enable-libx264 --enable-libvpx --enable-libtheora --enable-libgsm --enable-libspeex --enable-postproc --enable-shared --enable-x11grab --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libschroedinger --enable-libopenjpeg --enable-librtmp --enable-libpulse --enable-gpl --enable-version3 --enable-runtime-cpudetect --disable-debug --disable-static libavutil 51. 35.100 / 51. 35.100 libavcodec 53. 61.100 / 53. 61.100 libavformat 53. 32.100 / 53. 32.100 libavdevice 53. 4.100 / 53. 4.100 libavfilter 2. 61.100 / 2. 61.100 libswscale 2. 1.100 / 2. 1.100 libswresample 0. 6.100 / 0. 6.100 libpostproc 52. 0.100 / 52. 0.100 </code></pre>
 

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