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• saving H.264 encoded images with libavcodec

  8 octobre 2011, par user846400

  I am getting H.264 images from an IP camera and want to save the encoded images (without decoding). I am using output-example.c from ffmpeg (libavformat/output-example.c) for this purpose. For Saving the raw H.264 image, I do the following :

  AVPacket pkt;
  
  av_init_packet(&pkt);
  
  if (c->coded_frame->pts != AV_NOPTS_VALUE)
  
          pkt.pts= av_rescale_q(c->coded_frame->pts, c->time_base, st->time_base);
  
  if(c->coded_frame->key_frame)
  
          pkt.flags |= PKT_FLAG_KEY;
  
  pkt.stream_index= st->index;
  
  pkt.data= (uint8_t *)ulAddr;//video_outbuf;
  
  pkt.size= out_size;
  
  save_image(pkt.data, out_size);

  Where ulAddr is the address pointer to the image and out_size is the image size. Instead of saving the images to a media video file, I want to save the individual images. save_image function simply uses basic fopen and fwrite functions for saving the images. If I decode the frame and then save, everything works fine. But I have problem saving the encoded frames. The encoded frames are saved with a very small size and then they cannot be decoded.
  Is there anything wrong ? I will really appreciate any help in this regard.

• Splitting odd and even frames in Gstreamer

  4 avril 2014, par user3498379

  I am building an application whereby I need to split a videostream(RTSP/MJPEG) into individual frames. The extracted frames then need to be put into two named pipes. I need to alternate the frames between two named pipes, i.e. even frames go to pipe one and odd frames go to pipe 2. I have been able to achieve this with ffmpeg using the following command :

  ffmpeg -i "rtsp://<ipaddress>/axis-media/media.amp?videocodec=jpeg" -vf select="mod(n-1\,2)" -vcodec mjpeg -f avi -y  -vf select="not(mod(n-1\,2))" -vcodec mjpeg -f avi -y 
  
  </ipaddress>

  However I have run into an RTP packet size issue with ffmpeg when using large resolutions e.g. 2048x1536. My question is ; is there a gstreamer equivalent command ? I have the basic gstreamer command which extracts images :

   gst-launch rtspsrc location=rtsp://<ipaddress>/axis-media/media.amp?videocodec=jpeg ! decodebin2 ! jpegenc ! multifilesink location="frame%d.jpg"
  
  </ipaddress>

  But now I need the additional piece, any help will be much appreciated.

• How to fade video using a custom curve function in ffmpeg ?

  2 avril 2018, par Zoltan

  I would like to fade out a video using a different transition curve than what the fade filter uses (which is probably linear).

  For audio, I can easily choose from a wide variety of curves that the afade filter provides, or I can supply a custom expression to the volume filter, like (sin(PI/2 * min(1\, max(-1\, 1/2 * (t - 3)))) + 1)/2. For video, however, I could not find similar possibilities.

  Based on its description, it seems to me that the geq filter could be misused to achieve this, but I couldn’t get it to work. Additionally, it is very slow, probably because it works on individual pixels, even though the expression only depends on time.