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• FFMPEG h264 grey frame and artifacts at beginning

  28 novembre 2011, par marce002

  I'm splitting my "zi6 quicktime mov" hd videos, I have 250 clips of around 10 or 15 seconds each, from lot of places, locationes around the globe and want to combine them in a single big clip.

  I can merge them very good with "mkvmerge".

  The problem is that the first frames of all videos in the collection (splitted with ffmpeg), are gray or with artifacts at beggining, I do not know how to explain, maybe wrong ffmpeg commands, I'm doing this (with batch command line, which is great / fast for me) :

  =======begin of batch file

  ffmpeg -i jockey_club_fpv.mov -ss 00:00:17 -t 00:00:24 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3a.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:04:40 -t 00:00:20 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3b.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:05:35 -t 00:01:00 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3c.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:07:11 -t 00:00:10 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3d.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:07:45 -t 00:00:21 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3e.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:08:47 -t 00:00:05 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3f.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:09:18 -t 00:00:10 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3g.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:09:35 -t 00:00:09 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3h.mov
  
  ffmpeg -i jockey_club_fpv.mov -ss 00:10:07 -t 00:00:16 -g 1 -sameq -vcodec copy -vf fade=in:0:30 partes3i.mov
  
  mkvmerge -o join4.mov partes3a.mov + partes3b.mov + partes3c.mov + partes3d.mov + partes3e.mov + partes3f.mov + partes3g.mov + partes3h.mov + partes3i.mov

  =======end of batch file

  Thanks a lot for any answer !!

• Cleaning up after av_frame_get_buffer

  4 novembre 2016, par Jason C

  There are two aspects of my question. I’m using libav, ffmpeg, 3.1.

  ---

  First, how do you appropriately dispose of a frame whose buffer has been allocated with av_frame_get_buffer ? E.g. :

  AVFrame *frame = av_frame_alloc();
  
  frame->width = ...;
  
  frame->height = ...;
  
  frame->format = ...;
  
  av_frame_get_buffer(frame, ...);

  Do any buffers have to be freed manually, beyond the call to av_frame_free(frame) ? The documentation doesn’t mention anything special, but in my experience the ffmpeg documentation often leaves out important details, or at least hides them in places far away from the obvious spots. I took a look at the code for av_frame_free and av_frame_unref but it branched out quite a bit and I couldn’t quite determine if it covered everything.

  ---

  Second, if something beyond av_frame_free needs to be done, then is there any catch-all way to clean up a frame if you don’t know how its data has been allocated ? For example, assuming someBuffer is already allocated with the appropriate size :

  AVFrame *frame2 = av_frame_alloc();
  
  frame2->width = ...;
  
  frame2->height = ...;
  
  frame2->format = ...;
  
  av_image_fill_arrays(frame2->data, frame2->linesize, someBuffer, 
  
                       frame2->format, frame2->width, frame2->height, 1);

  Is there a way to free both frame and frame2 in the above examples using the exact same code ? That is frame and its data should be freed, and frame2 should be freed, but not someBuffer, since libav did not allocate it.

• How to averagely extract frames from a video using ffmpeg by specifying "fps"

  14 juin 2021, par alanzzz

  I have a job of using ffmpeg to extract the frames averagely from a video, with different fps. I use this command for it.

  


  ffmpeg -i input.mp4 -r specified_fps -q:v 2 image %4d.png

  


  And I have 3 questions about this task.

  


  

  1. what I expect is that if I double the fps, the number of extracted frames will also get doubled. However, that's not the case. Take one of the input videos as an example.

  


  


  video info

  


  

  • Duration : 1min18s

  


  • Total number of frames : 2340

  


  • Frame rate mode : constant (CFR)

  


  • Frame rate : 30.0 FPS

  


  


  Config setting & results

  


  

  • FPS=1 => number of frames=80

  


  • FPS=2 => number of frames=158 (2x80-2)

  


  • FPS=3 => number of frames=236 (3x80-4)

  


  • FPS=5 => number of frames=392 (5x80-8)

  


  


  Is it possible for me to get the exact doubled number of frames when fps get doubled ? In such case, number of frames is 160 for FPS=2, 240 for FPS=3, 400 for FPS=5.

  


  


  2. I check for the output images, the extracted frames in different fps are totally different from each other. In other words, for example, the 1st image for fps=1 is not the same as the 1st image for fps=2. Is that legitimate ? And is it possible for me the get some identical images for different fps ?

     


  


  3. The last problem is that for some videos I use, the difference between the 1st and 2nd image is different from the difference between the 2nd and 3rd. While for the remaining images, the differences become average. To be specific, there is only a slight change from 1st to 2nd frame, while for 2nd to 3rd, 3rd to 4th, and so on, the changes are the same, which is normally distributed according to the specified FPS. I am wondering why such a case happens ? Does it related to the I-frame, B-frame, P-frame, GOP or IDR ?

     


  


  


  I am new to this field and cannot find some useful info from other places. I've tried my best to describe my questions clearly. Feel free to leave some comments. Any help would do me a great favor. Thanks in advance !