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• avcodec/speexdec : Consider mode in frame size check

  26 décembre 2021, par Michael Niedermayer

  avcodec/speexdec : Consider mode in frame size check
  No speex samples with non default frame sizes are known (to me)
  
  the official speexenc seems to only generate the 3 default ones.
  
  Thus it may be that the fuzzer samples where the first non default
  
  values encountered by the decoder.
  
  Possibly the "<" should be " !="
  Fixes : out of array access
  
  Fixes : 42821/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SPEEX_fuzzer-5640695772217344
  Found-by : continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/speexdec.c

• three ways to achieve an H264 file

  18 mars 2016, par Kindermann

  here I have three ways to get an H264 file, like all forensic scientists, I am very curious about the differences between them :

  1.

  ffmpeg -i video.mp4 video.h264

  2.

  ffmpeg -i video.mp4 -vcodec copy -an -f h264 video.h264

  3. Using the example "demuxing_decoding.c" provided on the ffmpeg official website :
  http://ffmpeg.org/doxygen/trunk/demuxing_decoding_8c-example.html

  Obviously, the first one does the transformation, and the second one does the demuxing. They render different H264 files which however have similar file sizes(in my case, it’s about say 24 MB). Suprisingly, the third one, which is also supposed to do the demuxing job, renders an H264 file with 8.4 GB ! Why ?

  What I wondered is really, how the interiors of these three methods work ?(The third one is already in source code, therefore it’s quite easy to have an insight) What about the first two commands ? What APIs are called when executing these two commands and how those APIs are called(namely, in what kind of sequences they are called) and things like that.
  One thing that is also important to me is, i have no idea how I can trace the execution routines of ffmpeg command lines. I want to see what’s going on behind ffmpeg commands in source code version. Is it possible ?

  I appreciate any comment.

• Process GIF using FFmpeg libraries - can't find parser at av_parser_init

  24 novembre 2018, par natario

  I am playing with ffmpeg libs, namely libswscale and libavcodec for now. My goal is resize GIF files. From my ridiculous understanding, I think I need to

  • decode the GIF and get an AVFrame
  • process the frame with libswscale
  • encode again into GIF

  But I am stuck at step 1. Based on official sample at https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/decode_video.c , I need to get a parser :

  codec = avcodec_find_decoder(AV_CODEC_ID_GIF);
  
  parser = av_parser_init(codec->id);

  But no parser is found. I am not touching parser in my configure call, so I take all :

  Enabled parsers:
  
  aac                       cavsvideo                 dvbsub                    h263                      mpegvideo                 sipr                      xma
  
  aac_latm                  cook                      dvd_nav                   h264                      opus                      tak
  
  ac3                       dca                       dvdsub                    hevc                      png                       vc1
  
  adx                       dirac                     flac                      mjpeg                     pnm                       vorbis
  
  av1                       dnxhd                     g729                      mlp                       rv30                      vp3
  
  avs2                      dpx                       gsm                       mpeg4video                rv40                      vp8
  
  bmp                       dvaudio                   h261                      mpegaudio                 sbc                       vp9

  What am I doing wrong ? If this is the wrong approach, what is the correct one ?