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• cvCreateFileCapture always returns "NULL"

  4 août 2012, par user1553247

  I am making an iphone-app with Xcode 4.3.3 and OpenCV 2.4

  I used that "cvCreateFileCapture("simtom.mp4")" to get frame from '.mp4' file but unfortunately, cvCreateFileCapture() always returns "NULL".

  What is the problem ?

  Here is my source code.

   CvCapture *m_pMusicVideo;     
  
  
  
   m_pMusicVideo = cvCreateFileCapture("simtom.mp4");

• ffmpeg - avcodec_decode_audio3 always returns 0 with aac decoding on android

  26 novembre 2011, par Android007

  I am writing an audio decoder based on ffmpeg for android, where I have to decode aac audio, but because of some reason it always returns 0 bytes decoded.

  Looks like I pass everything right. Can anybody tell me what went wrong in my case.I copied code from ffplay.c.
  What is the reason avcodec_decode_audio3 function always returns zero ?

  Here is the code from ffplay.c :

  AVPacket *pkt_temp = &is->audio_pkt_temp;
  
      AVPacket *pkt = &is->audio_pkt;
  
      AVCodecContext *dec= is->audio_st->codec;
  
      int n, len1, data_size;
  
      double pts;
  
  
  
            data_size = sizeof(is->audio_buf1);
  
          len1 = avcodec_decode_audio3(dec, (int16_t *)is->audio_buf1, &data_size, pkt_temp);
  
          if (len1 < 0) {
  
              pkt_temp->size = 0;
  
              break;
  
          } 
  
  
  
         if (data_size <= 0){
  
                     //This block always gets executed.
  
              continue;
  
      }

• Video concatenation using ffmpeg. Output video length is longer than inputs length

  28 décembre 2022, par Rostyslav Mosorov

  I have a problem with video mp4 concatenation using ffmpeg. I have two the same videos and I want to concatenate them. I created file inputs.txt and then used command :

  


  ffmpeg  -f concat -i inputs.txt -c copy mergedVideo.mp4

  


  Output :

  


  ffmpeg  -f concat -i inputs.txt -c copy mergedVideo.mp4
ffmpeg version 5.0.1 Copyright (c) 2000-2022 the FFmpeg developers
  built with clang version 12.0.1
  configuration: --prefix=/Users/runner/miniforge3/conda-bld/ffmpeg_1649114094397/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_pl --cc=arm64-apple-darwin20.0.0-clang --disable-doc --disable-openssl --enable-demuxer=dash --enable-gnutls --enable-gpl --enable-hardcoded-tables --enable-libfreetype --enable-libopenh264 --enable-neon --enable-libx264 --enable-libx265 --enable-libaom --enable-libsvtav1 --enable-libxml2 --enable-libvpx --enable-pic --enable-pthreads --enable-shared --disable-static --enable-version3 --enable-zlib --enable-libmp3lame --pkg-config=/Users/runner/miniforge3/conda-bld/ffmpeg_1649114094397/_build_env/bin/pkg-config --enable-cross-compile --arch=arm64 --target-os=darwin --cross-prefix=arm64-apple-darwin20.0.0- --host-cc=/Users/runner/miniforge3/conda-bld/ffmpeg_1649114094397/_build_env/bin/x86_64-apple-darwin13.4.0-clang
  libavutil      57. 17.100 / 57. 17.100
  libavcodec     59. 18.100 / 59. 18.100
  libavformat    59. 16.100 / 59. 16.100
  libavdevice    59.  4.100 / 59.  4.100
  libavfilter     8. 24.100 /  8. 24.100
  libswscale      6.  4.100 /  6.  4.100
  libswresample   4.  3.100 /  4.  3.100
  libpostproc    56.  3.100 / 56.  3.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x1561044a0] Auto-inserting h264_mp4toannexb bitstream filter
Input #0, concat, from 'inputs.txt':
  Duration: N/A, start: -0.064000, bitrate: 1424 kb/s
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], 1355 kb/s, 50 fps, 50 tbr, 12800 tbn
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 16000 Hz, mono, fltp, 68 kb/s
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
File 'mergedVideo.mp4' already exists. Overwrite? [y/N] y
Output #0, mp4, to 'mergedVideo.mp4':
  Metadata:
    encoder         : Lavf59.16.100
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 1355 kb/s, 50 fps, 50 tbr, 12800 tbn
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 16000 Hz, mono, fltp, 68 kb/s
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame=    0 fps=0.0 q=-1.0 size=       0kB time=00:00:00.06 bitrate=   6.0k[mov,mp4,m4a,3gp,3g2,mj2 @ 0x154f28b20] Auto-inserting h264_mp4toannexb bitstream filter
frame=  166 fps=0.0 q=-1.0 Lsize=     583kB time=00:00:03.39 bitrate=1407.4kbits/s speed= 179x    
video:550kB audio:29kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.737394%


  


  Unfortunately the result is different then I expected :
  
movies comparison

  


  The output is longer than the length of two inputs. Any thoughts ?

  


  Also I tried using different commands :

  


  ffmpeg  -f concat -i inputs.txt -c copy mergedVideo.mp4


  


  or set the framerate :

  


  ffmpeg -r 50 -f concat -i inputs.txt -c copy mergedVideo.mp4


  


  What is also weird that I have the same problem when using moviepy library.

  


  from moviepy.editor import VideoFileClip, concatenate_videoclips
videos = [VideoFileClip("0.mp4"), VideoFileClip("0.mp4")]
concatenate_videoclips(videos).write_videofile('mergedVideo.mp4')


  


  Update
ffprobe command for output file

  


  ffprobe -v error -select_streams v -show_entries stream=codec_name,time_base,start_pts,start_time,duration -of default=noprint_wrappers=1 mergedVideo.mp4 
codec_name=h264
time_base=1/12800
start_pts=0
start_time=0.000000
duration=3.380000


  


  For input :

  


  ffprobe -v error -select_streams v -show_entries stream=codec_name,time_base,start_pts,start_time,duration -of default=noprint_wrappers=1 0.mp4          
codec_name=h264
time_base=1/12800
start_pts=0
start_time=0.000000
duration=1.660000


  


  The duration supposed to be 2*1.66 = 3.32 and but it's 3.38.

  


  Content of the inputs.txt

  


  file '0.mp4'
file '0.mp4'