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• 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.

• ffmpeg, how to avoid audio drift when muxing audio and video

  1er mai 2023, par Monkeybus

  I use scrcpy to mirror my Android screen to my PC. I have to capture the audio via bluetooth.

  


  The result is two files. One .mkv and one .aac. They are both of equal length, possibly a second or two out.

  


  I mux them together, but the audio always drifts.

  


  I mux them together with the following command, $show is the bash variable for the video file.

  


  ffmpeg -i $show.mkv -ss -00:00:02 -i $show.aac -c:v copy -c:a copy -shortest $show.muxed.mkv


  


  The -ss sets the audio start time. I generally have to play around with this on a vid by vid basis. I can generally match the audio and video perfectly at the beginning of the file, but the audio will always drift over the course of the video.

  


• ffmpeg - filter_complex list too long

  2 mars 2016, par Baumi

  Let’s say I want to overlay a clock in the video using special font, color, etc to video that is aprox 30 min long. I end up with command :

  ffmpeg -y -i in.mp4 -filter_complex "
  
  [0:v]drawtext=fontfile=/var/www/sites/manage/elements/digital-7.ttf:text='00\:00':fontcolor=white@1.0:fontsize=26:x=100:y=65:enable='between(t,0,7)'[tmp];
  
  [tmp]drawtext=fontfile=/var/www/sites/manage/elements/digital-7.ttf:text='00\:01':fontcolor=white@1.0:fontsize=26:x=100:y=65:enable='between(t,7,8)'[tmp]; 
  
  [tmp]drawtext=fontfile=/var/www/sites/manage/elements/digital-7.ttf:text='00\:02':fontcolor=white@1.0:fontsize=26:x=100:y=65:enable='between(t,8,9)'[tmp]; 
  
  [tmp]drawtext=fontfile=/var/www/sites/manage/elements/digital-7.ttf:text='00\:03':fontcolor=white@1.0:fontsize=26:x=100:y=65:enable='between(t,9,10)'[tmp]; 
  
  [tmp]drawtext=fontfile=/var/www/sites/manage/elements/digital-7.ttf:text='00\:04':fontcolor=white@1.0:fontsize=26:x=100:y=65:enable='between(t,10,11)'[tmp];
  
  ......." 
  
  -map "[tmp]" -map 0:a -acodec copy -c:v h264 out.mp4

  This clock is not the only overlay I have so finally I have end up with command 216kB long but this I cannot even run in bash because of argument list being too long.

  I wanted to re-encode the video only once. Is there any other way I can do that ?

  Thanks !