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• Reasons for "Segmentation fault (core dumped)" when using Python extension and FFmpeg

  24 août 2021, par Christian Vorhemus

  I want to write a Python C extension that includes a function convertVideo() that converts a video from one format to another making use of FFmpeg 3.4.8 (the libav* libaries). The code of the extension is at the end of the question. The extension compiles successfully but whenever I open Python and want to call it (using a simple Python wrapper code that I don't include here), I get

  


  Python 3.7.10 (default, May  2 2021, 18:28:10)
[GCC 9.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import myModule
>>> myModule.convert_video("/home/admin/video.h264", "/home/admin/video.mp4")
convert 0
convert 1
Format raw H.264 video, duration -9223372036854775808 us
convert 2
Segmentation fault (core dumped)


  


  The interesting thing is, I wrote a simple helper program test_convert.cc that calls convertVideo() like so

  


  #include 
#include 

int convertVideo(const char *in_filename, const char *out_filename);

int main() {
  int res = convertVideo("/home/admin/video.h264", "/home/admin/video.mp4");
  return 0;
}


  


  and I compiled this program making use of the shared library that Python generates when building the C extension like so

  


  gcc test_convert.cc /usr/lib/python3.7/site-packages/_myModule.cpython-37m-aarch64-linux-gnu.so -o test_convert


  


  And it works ! The output is

  


  root# ./test_convert
convert 0
convert 1
Format raw H.264 video, duration -9223372036854775808 us
convert 2
convert 3
convert 4
convert 5
convert 6
Output #0, mp4, to '/home/admin/video.mp4':
    Stream #0:0: Video: h264 (High), yuv420p(tv, bt470bg, progressive), 1280x720 [SAR 1:1 DAR 16:9], q=2-31
convert 7


  


  The extension code looks like this

  


  #include 

#include 
#include 
#include 
#include 
#include 
#include 
#include 

extern "C"
{
#include "libavformat/avformat.h"
#include "libavutil/imgutils.h"
}

int convertVideo(const char *in_filename, const char *out_filename)
{
  // Input AVFormatContext and Output AVFormatContext
  AVFormatContext *input_format_context = avformat_alloc_context();
  AVPacket pkt;

  int ret, i;
  int frame_index = 0;
  printf("convert 0\n");
  av_register_all();
  printf("convert 1\n");
  // Input
  if ((ret = avformat_open_input(&input_format_context, in_filename, NULL,
                                 NULL)) < 0)
  {
    printf("Could not open input file.");
    return 1;
  }
  else
  {
    printf("Format %s, duration %lld us\n",
           input_format_context->iformat->long_name,
           input_format_context->duration);
  }
  printf("convert 2\n");
  if ((ret = avformat_find_stream_info(input_format_context, 0)) < 0)
  {
    printf("Failed to retrieve input stream information");
    return 1;
  }
  printf("convert 3\n");
  AVFormatContext *output_format_context = avformat_alloc_context();
  AVPacket packet;
  int stream_index = 0;
  int *streams_list = NULL;
  int number_of_streams = 0;
  int fragmented_mp4_options = 0;
  printf("convert 4\n");
  avformat_alloc_output_context2(&output_format_context, NULL, NULL,
                                 out_filename);
  if (!output_format_context)
  {
    fprintf(stderr, "Could not create output context\n");
    ret = AVERROR_UNKNOWN;
    return 1;
  }
  printf("convert 5\n");
  AVOutputFormat *fmt = av_guess_format(0, out_filename, 0);
  output_format_context->oformat = fmt;

  number_of_streams = input_format_context->nb_streams;
  streams_list =
      (int *)av_mallocz_array(number_of_streams, sizeof(*streams_list));

  if (!streams_list)
  {
    ret = AVERROR(ENOMEM);
    return 1;
  }
  for (i = 0; i < input_format_context->nb_streams; i++)
  {
    AVStream *out_stream;
    AVStream *in_stream = input_format_context->streams[i];
    AVCodecParameters *in_codecpar = in_stream->codecpar;
    if (in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO &&
        in_codecpar->codec_type != AVMEDIA_TYPE_VIDEO &&
        in_codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE)
    {
      streams_list[i] = -1;
      continue;
    }
    streams_list[i] = stream_index++;

    out_stream = avformat_new_stream(output_format_context, NULL);
    if (!out_stream)
    {
      fprintf(stderr, "Failed allocating output stream\n");
      ret = AVERROR_UNKNOWN;
      return 1;
    }
    ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar);
    if (ret < 0)
    {
      fprintf(stderr, "Failed to copy codec parameters\n");
      return 1;
    }
  }
  printf("convert 6\n");
  av_dump_format(output_format_context, 0, out_filename, 1);
  if (!(output_format_context->oformat->flags & AVFMT_NOFILE))
  {
    ret = avio_open(&output_format_context->pb, out_filename, AVIO_FLAG_WRITE);
    if (ret < 0)
    {
      fprintf(stderr, "Could not open output file '%s'", out_filename);
      return 1;
    }
  }
  AVDictionary *opts = NULL;
  printf("convert 7\n");
  ret = avformat_write_header(output_format_context, &opts);
  if (ret < 0)
  {
    fprintf(stderr, "Error occurred when opening output file\n");
    return 1;
  }
  int n = 0;

  while (1)
  {
    AVStream *in_stream, *out_stream;
    ret = av_read_frame(input_format_context, &packet);
    if (ret < 0)
      break;
    in_stream = input_format_context->streams[packet.stream_index];
    if (packet.stream_index >= number_of_streams ||
        streams_list[packet.stream_index] < 0)
    {
      av_packet_unref(&packet);
      continue;
    }
    packet.stream_index = streams_list[packet.stream_index];

    out_stream = output_format_context->streams[packet.stream_index];

    out_stream->codec->time_base.num = 1;
    out_stream->codec->time_base.den = 30;

    packet.pts = n * 3000;
    packet.dts = n * 3000;
    packet.duration = 3000;

    packet.pos = -1;

    ret = av_interleaved_write_frame(output_format_context, &packet);
    if (ret < 0)
    {
      fprintf(stderr, "Error muxing packet\n");
      break;
    }
    av_packet_unref(&packet);
    n++;
  }

  av_write_trailer(output_format_context);
  avformat_close_input(&input_format_context);
  if (output_format_context &&
      !(output_format_context->oformat->flags & AVFMT_NOFILE))
    avio_closep(&output_format_context->pb);
  avformat_free_context(output_format_context);
  av_freep(&streams_list);
  if (ret < 0 && ret != AVERROR_EOF)
  {
    fprintf(stderr, "Error occurred\n");
    return 1;
  }
  return 0;
}
// PyMethodDef and other orchestration code is skipped


  


  What is the reason that the code works as expected in my test_convert but not within Python ?

  


• gcc "relocation R_X86_64_PC32 against symbol `ff_M24A'" error when linking statically against ffmpeg on linux

  15 juillet 2021, par YB_Evil

  I am trying to build a JNI shared library which statically links to ffmpeg.

  



  But at the linking stage, gcc fails with the following error :

  



  /usr/bin/ld: ./lib_lin64/libswscale.a(swscale.o): relocation R_X86_64_PC32 against symbol `ff_M24A' can not be used when making a shared object; recompile with -fPIC


  



  I am using the following commands to compile my jni library :

  



  gcc -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -I ./include -fPIC -c *.c
  
gcc -shared -Wl,--no-undefined -o libnv_avc_dec.so *.o -Wl,-Bstatic -L./lib_lin64 -lavcodec -lavutil -lswresample -lswscale -Wl,-Bdynamic -lm


  



  And I only use h264 decoding feature, so I am also building ffmpeg from source with the minimal required feature set. The ./configure command I use is :

  



  ./configure \
--enable-pic --prefix=ffmpeg-dist \
--disable-debug --enable-version3 --enable-gpl \
--disable-everything --enable-hwaccel=h264_vdpau --enable-hwaccel=h264_vaapi --enable-hwaccel=h264_qsv --enable-hwaccel=h264_mmal \
--enable-decoder=h264 --enable-decoder=h264_vdpau --enable-decoder=h264_crystalhd --enable-decoder=h264_mmal --enable-decoder=h264_qsv \
--disable-iconv --disable-securetransport --disable-xlib --disable-zlib --disable-lzma  --disable-bzlib  --disable-doc --disable-programs --disable-avformat --disable-avfilter --disable-postproc


  



  So, as I understand, the linker tells me that ffmpeg should be compiled with -fPIC flag in order to make a shared library. But I believe that I've already done so by specifying the —enable-pic configure flag. And I am pretty much stuck here because I am not very familiar with autotools, nor with ffmpeg build process in particular.

  



  If this is the issue of ffmpeg .a libs not being compiled with -fPIC flag, how can i force it ? And if this is not the case, what am i doing wrong and how can i fix this error ?

  



  Environment details : Ubuntu 14.04.3 64-bit in Virtualbox, gcc 4.8.5 and 5.3 (both give the same results), ffmpeg v.2.8.5

  


• Getting "TypeError : must be real number, not NoneType" whenever trying to run write_videofile to a clip in moviepy

  9 novembre 2024, par Sato

  Example code :

  


  from moviepy.editor import *
clip = VideoFileClip('video.mp4')
clip.write_videofile('video2.mp4', fps=30)


  


  After showing the following messages, showing that the video is being built and written,

  


  Moviepy - Building video video2.mp4.
Moviepy - Writing video video2.mp4


  


  The following error message occurs :

  


  Traceback (most recent call last):&#xA;  File "<stdin>", line 1, in <module>&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\decorator.py", line 232, in fun&#xA;    return caller(func, *(extras &#x2B; args), **kw)&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\moviepy\decorators.py", line 54, in requires_duration&#xA;    return f(clip, *a, **k)&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\decorator.py", line 232, in fun&#xA;    return caller(func, *(extras &#x2B; args), **kw)&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\moviepy\decorators.py", line 135, in use_clip_fps_by_default&#xA;    return f(clip, *new_a, **new_kw)&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\decorator.py", line 232, in fun&#xA;    return caller(func, *(extras &#x2B; args), **kw)&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\moviepy\decorators.py", line 22, in convert_masks_to_RGB&#xA;    return f(clip, *a, **k)&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\moviepy\video\VideoClip.py", line 300, in write_videofile&#xA;    ffmpeg_write_video(self, filename, fps, codec,&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\moviepy\video\io\ffmpeg_writer.py", line 213, in ffmpeg_write_video&#xA;    with FFMPEG_VideoWriter(filename, clip.size, fps, codec = codec,&#xA;  File "C:\Users\User\Anaconda3\lib\site-packages\moviepy\video\io\ffmpeg_writer.py", line 88, in __init__&#xA;    &#x27;-r&#x27;, &#x27;%.02f&#x27; % fps,&#xA;TypeError: must be real number, not NoneType&#xA;</module></stdin>

  


  This occurs whenever I try to perform write_videofile to any kinds of clip in moviepy. It is strange since the exact same code worked for me yesterday, but suddenly not anymore today. Are there any suggestions what the cause is and how to resolve this ?