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• libavfilter : Adds on the fly generation of default DNN models for tensorflow backend...

  27 juillet 2018, par Sergey Lavrushkin

  libavfilter : Adds on the fly generation of default DNN models for tensorflow backend instead of storing binary model.
  Signed-off-by : Pedro Arthur <bygrandao@gmail.com>
  

  • [DH] libavfilter/dnn_backend_native.c
  • [DH] libavfilter/dnn_backend_tf.c
  • [DH] libavfilter/dnn_espcn.h
  • [DH] libavfilter/dnn_srcnn.h
  • [DH] libavfilter/vf_sr.c

• merging images to create video using ffmpeg

  3 octobre 2017, par Md Jawed Shamshedi

  I am creating a video from images using ffmpeg. I am using a file that contains the list of images as

  file 'C:\wamp64\www\test\public\userFolder\media\nature3.jpg'
  
  file 'C:\wamp64\www\test\public\userFolder\media\img_001.jpg'
  
  file 'C:\wamp64\www\test\public\userFolder\media\img_003.jpg'
  
  file 'C:\wamp64\www\test\public\userFolder\media\img_006.jpg'
  
  file 'C:\wamp64\www\test\public\userFolder\media\nature3.jpg'
  
  file 'C:\wamp64\www\test\public\userFolder\media\nature4.jpg'

  I am using the following command to create video

  ffmpeg.exe -y -r 1/10 -f concat -safe 0 -i "imagepaths.txt" -c:v libx264  -s 920x640 "Jawedout.mp4"

  The video is being created but the start of video is blank. The video show dark black screen for few secs then show the first image mentioned in file.

  However, if the change the command to

  ffmpeg.exe -y -f concat -safe 0 -i "imagepaths.txt" -c:v libx264 -vf "fps=25,format=yuv420p" -s 920x640 "Jawedout.mp4"

  Then in video I am not seeing first image and last image.

• FFmpeg what exactly is the filtergraph pipeline like during transcoding ?

  8 septembre 2017, par Jeff Gong

  I have been studying the source code for FFmpeg to attempt to understand its threading model and how it processes inputs. For example, when I run a command like :

  ffmpeg -i video.mp4 -s hd720 -c:v libx264 --preset medium -c:a aac -profile:v main -r 60 -f null /dev/null

  The input itself is irrelevant, but I am trying to understand how the transcoding pipeline works. In the source code, I see that the main steps occur in the functions transcode and transcode_step.

  It seems like for a single input, a single frame is read in, decoded, encoded, and written out. The process is obviously very complex but what I am really not understanding is what FFmpeg is doing when it attempts to build out a filtergraph. For example, in transcode_step of ffmpeg.c, there is the following code that happens right after an output stream has been selected :

  if (ost->filter && !ost->filter->graph->graph) {
  
      if (ifilter_has_all_input_formats(ost->filter->graph)) {
  
          ret = configure_filtergraph(ost->filter->graph);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Error reinitializing filters!\n");
  
              return ret;
  
          }
  
      }
  
  }

  Does this only apply if I specify a specific series of filtering options to FFmpeg, like the one in this link ? For the sample command I input above, is this code still executed ?

  One last other question I had was for the case where I run an FFmpeg instance with a single input but multiple outputs (perhaps different variants for transcoding). In this scenario, does a single phase of transcode_step take in an input frame and send that frame through decoding and encoding for only a single one of the outputs ? Or does it take a frame at a time and process this frame for each of the outputs we have specified ?