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• Display stream with FFmpeg, python and opencv

  23 février, par Ηλίας Κωνσταντινίδης

  Situation :
I have a basler camera connected to a raspberry pi, and I am trying to livestream it's feed with FFmpg to a tcp port in my windows PC in order to monitor whats happening in front of the camera.

  


  Things that work :
I manage to set up a python script on the raspberry pi which is responsible for recording the frames, feed them to a pipe and streaming them to a tcp port. From that port, I am able to display the stream using FFplay.

  


  My problem :
FFplay is great for testing out quickly and easily if the direction you are heading is correct, but I want to "read" every frame from the stream, do some processing and then displaying the stream with opencv. That, I am not able to do yet.

  


  Minimaly reprsented, that's the code I use on the raspberry pi side of things :

  


  command = ['ffmpeg',
           '-y',
           '-i', '-',
           '-an',
           '-c:v', 'mpeg4',
           '-r', '50',
           '-f', 'rtsp',
           '-rtsp_transport',
           'tcp','rtsp://192.168.1.xxxx:5555/live.sdp']

p = subprocess.Popen(command, stdin=subprocess.PIPE) 

while camera.IsGrabbing():  # send images as stream until Ctrl-C
    grabResult = camera.RetrieveResult(100, pylon.TimeoutHandling_ThrowException)
    
    if grabResult.GrabSucceeded():
        image = grabResult.Array
        image = resize_compress(image)
        p.stdin.write(image)
    grabResult.Release() 



  


  On my PC if I use the following FFplay command on a terminal, it works and it displays the stream in real time :

  


  ffplay -rtsp_flags listen rtsp://192.168.1.xxxx:5555/live.sdp?tcp

  


  On my PC if I use the following python script, the stream begins, but it fails in the cv2.imshow function because I am not sure how to decode it :

  


  import subprocess
import cv2

command = ['C:/ffmpeg/bin/ffmpeg.exe',
           '-rtsp_flags', 'listen',
           '-i', 'rtsp://192.168.1.xxxx:5555/live.sdp?tcp?', 
           '-']

p1 = subprocess.Popen(command, stdin=subprocess.PIPE, stdout=subprocess.PIPE)

while True:
    frame = p1.stdout.read()
    cv2.imshow('image', frame)
    cv2.waitKey(1)


  


  Does anyone knows what I need to change in either of those scripts in order to get i to work ?

  


  Thank you in advance for any tips.

  


• FFMPEG tee muxer giving "Output file #0 does not contain any stream"

  31 août 2020, par Giorgi Aptsiauri

  I am trying to create two streams : one is mpegts UDP stream another - rtmp to Twitch servers.

  


  This command works :

  


    ffmpeg -threads:v 2 -threads:a 16 -filter_threads 2 -thread_queue_size 16 -y \
 -f dshow -video_size 1920x1080 -pixel_format uyvy422 -framerate 25 -rtbufsize 500M -i video="Decklink Video Capture" \
 -f dshow -rtbufsize 100M -i audio="Decklink Audio Capture" \
 -preset ultrafast -c:v libx264 -tune zerolatency -b:v 900k -map 0:v:0 -f mpegts udp://127.0.0.1:5555 \ 
 -pix_fmt yuv420p -c:v libx264 -crf 20 -tune zerolatency -f flv rtmp://live-fra05.twitch.tv/app/stream_key


  


  But it requires double the encoding CPU power.

  


  So, following this, I rewrote the command like this :

  


  ffmpeg -threads:v 2 -threads:a 16 -filter_threads 2 -thread_queue_size 16 -y \
 -f dshow -video_size 1920x1080 -pixel_format uyvy422 -framerate 25 -rtbufsize 500M -i video="Decklink Video Capture" \
 -f dshow -rtbufsize 100M -i audio="Decklink Audio Capture" \
 -preset ultrafast -c:v libx264 -tune zerolatency -b:v 900k \
 -f tee "[select=\'0:v:0\':f=mpegts]udp://127.0.0.1:5555|[select=\'0:v:0,1:a:0\':f=flv]rtmp://live-fra05.twitch.tv/app/stream_key"


  


  By writing -f tee "[select=\'0:v:0\':f=mpegts]udp://127.0.0.1:5555|[select=\'0:v:0,1:a:0\':f=flv]rtmp://live-fra05.twitch.tv/app/stream_key", I mean :

  


  

  • create UDP stream at udp ://127.0.0.1:5555 and only include video stream from "Decklink Video Capture"

  


  • create RTMP stream where we include the same video stream as above and also the audio stream from "Decklink Audio Capture"

  


  


  I get the error message :

  


  Output file #0 does not contain any stream


  


  How do I fix this ? I assume I made a mistake in the command.

  


• Gnuplot how to set a variable to standard-input if not passed

  27 août 2020, par DDS

  I have a gnuplot script (plot.script) that is invoked like

  


  C:> ffmpeg -i '.\my_awesome_audio_file.wav' -filter_complex aformat=channel_layouts=mono -acodec pcm_s16le -ar 4000 -f data - | gnuplot -e "fileout='plot';fileformat='png';wid=500;" .\plot.script        


  


  Now I'd want to default filein variable to stdin if it is not passed as argument. This because I want to be able to call this script as a 1-liner command with ffmpeg data generation and also as step-by-step procedure

  


  My idea was to use

  


  if(!exists('filein')){
filein = '-';
}


  


  but this throws warning: Skipping data file with no valid points

  


  if i print the variable datafile I got - (I expected something like stdin).

  


  this is the plot.script script :

  


  
if(!exists('filein')){
    filein = '-';
    }

if (!exists("hei")){
    hei = 4444;
    }
if (!exists("wid")){
    wid = 5555;
    }
if(!exists("fileformat")){
     fileformat = 'png';
     }
if(!exists("fileout")){
     fileout = 'risultato';
   }
   
fileout = fileout . '.' . fileformat;
   
if(!exists("dataformat")){
    dataformat = '%int16';
    }
if(fileformat eq 'png'){
  set terminal png transparent size larghezza,altezza;
  
  }else{
  set terminal fileformat size wid,hei;
  }
  set output fileout;
  unset key;
  unset tics;
  unset border;
  set lmargin 0;
  set rmargin 0;
  set tmargin 0;
  set bmargin 0;


print filein;
plot filein binary filetype=bin format=dataformat endian=little array=1:0 with lines linecolor "0x009900";


  


  But I also want to call this command-by-command :
generate the data-file :

  


  c:> ffmpeg -i '.\my_awesome_audio_file.wav' -filter_complex aformat=channel_layouts=mono -acodec pcm_s16le -ar 4000 -f data audio.dat


  


  plot the data :

  


  c:> gnuplot -e "filein='audio.dat';fileout='plot';fileformat='png';wid=500;" .\plot.script