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• Creating Video and Streaming Command Line

  31 juillet 2024, par Brindha Kanniah

  Currently, using ffmpeg, I am using two commands on my Terminal to :

  



  1) create a video from a bunch of images :

  



  ffmpeg -r 60 -f image2 -s 1920x1080 -i rotated-pano_frame%05d_color_corrected_gradblend.jpg -vcodec libx264 -crf 25 -pix_fmt yuv420p test.mp4


  



  2) stream the video to a udp address :

  



  ffmpeg -re -i test.mp4 -c copy -f flv udp://127.0.0.1:48550


  



  I am trying to combine both these instructions into one command line instruction, using &&, as suggested in the answer to a previous question of mine :

  



  ffmpeg -r 60 -f image2 -s 1920x1080 -i rotated-pano_frame%05d_color_corrected_gradblend.jpg -vcodec libx264 -crf 25 -pix_fmt yuv420p test.mp4 \
&& ffmpeg -re -i test.mp4 -c copy -f flv udp://127.0.0.1:48550


  



  but am encountering an error which prevents streaming :

  



  [flv @ 0x7fa2ba800000] video stream discovered after head already parsed.


  



  Thoughts on a different command line syntax to join the two instructions, different ffmpeg instruction (filters perhaps ?), and why I am getting the error ?

  


• Drop outgoing FFmpeg stream depending on the input stream's speed

  13 mars 2021, par aroquev00

  This is my situation : I have an incoming video stream, and I reprocess it with FFmpeg to generate another stream with my required encoding characteristics. However, I cannot always control the quality of the incoming source stream (network issues, CPU issues from sender, etc.), and in these situations my outgoing stream starts to freeze (because there is not enough incoming data from the source stream), but it does not stop : the ffmpeg process continues to run and if the source stream recovers, then my stream recovers.

  


  What I would like to achieve is that when the input speed gets below a given treshold (say 0.9x), my stream should stop (terminate ffmpeg process, like it does when the input stream is non existent).

  


  I'm new to FFmpeg in general, and I wanted to know if there is an easy way to achieve this, or if I should implement a program that continuously parses the ffmpeg command's output to identify when the stream speed is below what I need it to be.

  


  If it helps in any way, this is my current ffmpeg stream command.

  


  ffmpeg -i http://localhost:1234 -c:v libx264 -preset superfast -maxrate 2200k -b:v 2000k -bufsize 2200k -g 60 -c:a aac -b:a 160k -ac 2 -ar 44100 -f flv http://myDestAddress:5678

  


  Thanks a lot for the help in advance !

  


• Extract frames from a video results in abnormaly more frames for each fps by using ffmpeg

  15 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. I get 2 extra frames for all the sample factors (80 / 158 / 236 / 392 v.s. 78 / 156 / 234 / 390). Does it related to the mechanism of picking/dropping frames when extracting frames from a video？ (credit to @Tom Yan)

  


  


  video info

  


  

  • Duration : 1min18s

  


  • Frame rate mode : constant (CFR)

  


  • Frame rate : 30.0 FPS

  


  • Total number of frames : 2340

  


  


  Config setting & results

  


  





  


  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  FPS	Actual num of frames	correct num of frames
  1	80	78
  2	158	156
  3	236	234
  5	392	390

  


  


  


  2. I check for the output images, the extracted frames for 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 relate 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 !