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• How can I split a series of clips from a video and then stitch them together without audio or video gaps ?

  16 avril 2020, par Dr. Cyber Sec

  I'm developing an application where I take a video and (1) split it up into a bunch of 1 second chunks. Then, I need to (2) stitch a subset of those chunks back together, resulting in a slice of the original video.

  



  For example, let's say I have an original, 10s clip. I split it up into 1s chunks for each second (a clip from 0s to 1s, a clip from 1s to 2s, etc.). I now need to stitch, say, seconds 2-4 together into one video.

  



  I'm currently attempting both steps using ffmpeg.

  



  For clip-cutting :

  



  ffmpeg -ss 33 -i video.ts -t 1 33to34.ts


  



  This should seek to second 33 and output a 1s clip duration, yielding a video clip containing seconds 33-34 of the original video. I noticed that ffmpeg doesn't always seek accurately, so after following the instructions in this post, which says to manually add keyframes to the parts of the video you want to cut, I tried this :

  



  First, setting the keyframes :

  



  ffmpeg -i video.ts -force_key_frames 00:00:01.000,00:00:02.000,00:00:03.000,00:00:04.000 out.ts


  



  And then cutting the clips as I did before with the new output clip.

  



  While this did get the videos to be exactly 1s long each, (which I wanted) there is a small gap (just a slight jitter) in audio when I combine the clips back together. I cannot have this, and am looking for a solution.

  



  Can anyone help me understand why this is happening and help me find a solution ? Thank you so much in advance.

  


• iPhone - A problem with decoding H264 using ffmpeg

  25 mars 2012, par HAPPY_TIGER

  I am working with ffmpeg to decode H264 stream from server.

  I referenced DecoderWrapper from http://github.com/dropcam/dropcam_for_iphone.

  I compiled it successfully, but I don't know how use it.

  Here are the function that has problem.

  - (id)initWithCodec:(enum VideoCodecType)codecType 
  
           colorSpace:(enum VideoColorSpace)colorSpace 
  
                width:(int)width 
  
               height:(int)height 
  
          privateData:(NSData*)privateData {
  
      if(self = [super init]) {
  
  
  
          codec = avcodec_find_decoder(CODEC_ID_H264);
  
          codecCtx = avcodec_alloc_context();
  
  
  
          // Note: for H.264 RTSP streams, the width and height are usually not specified (width and height are 0).  
  
          // These fields will become filled in once the first frame is decoded and the SPS is processed.
  
          codecCtx->width = width;
  
          codecCtx->height = height;
  
  
  
          codecCtx->extradata = av_malloc([privateData length]);
  
          codecCtx->extradata_size = [privateData length];
  
          [privateData getBytes:codecCtx->extradata length:codecCtx->extradata_size];
  
          codecCtx->pix_fmt = PIX_FMT_YUV420P;
  
  #ifdef SHOW_DEBUG_MV
  
          codecCtx->debug_mv = 0xFF;
  
  #endif
  
  
  
          srcFrame = avcodec_alloc_frame();
  
          dstFrame = avcodec_alloc_frame();
  
  
  
          int res = avcodec_open(codecCtx, codec);
  
          if (res < 0)
  
          {
  
              NSLog(@"Failed to initialize decoder");
  
          }
  
      }
  
  
  
      return self;    
  
  }

  What is the privateData parameter of this function ? I don't know how to set the parameter...

  Now avcodec_decode_video2 returns -1 ;

  The framedata is coming successfully.

  How solve this problem.

  Thanks a lot.

• add black&silence to beginning of a video

  21 août 2020, par Richard

  Hi I am struggling to add black&silence to the begining of a video with ffmpeg. I did search a lot but they look too complex for me.
Below command is what I find to add black&silence to the end of of video, now how can I tune it to the beginning of a video ?

  


  ffmpeg -i input.mp4 -f lavfi -i color=s=1920x1080:d=10 -filter_complex [0:v][1]concat -af [0]apad -shortest output.mp4


  


  Looks I need to use adelay instead of apad, below is the command that makes sense to me, but the audio is not delayed.

  


  ffmpeg -i input.mp4 -f lavfi -i color=s=1920x1080:d=10 -filter_complex [1][0:v]concat -af [0]adelay=10  output.mp4


  


  Here is the input info and ffmpeg version :

  


  ffmpeg -i input.mp4 
ffmpeg version 4.2.1-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls     --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb     --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab     --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:01:00.00, start: 0.000998, bitrate: 2526 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080, 2394 kb/s, 24 fps, 24 tbr, 16k tbn, 48 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 124 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
At least one output file must be specified


  


  Thanks !