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• How to use ffmpeg to push my Unity3d process screenshot to nginx-rtmp server ?

  26 mars 2019, par Menghui

  I want to broadcast my Unity process screen.

  What I can think of is to use the Unity screenshot, then pipe png to the ffmpeg process, ffmpeg encodes png into h264 and pushes it to the server.

  How to use ffmpeg and named pipe to encod and push stream ?

  1. About png to h264, is this possible to push ? (But I can’t play server video stream with vlc)

  .\ffmpeg.exe -framerate 24 -i .\screenshot%03d.png -vcodec libx264 -acodec aac -strict -2 -f h264 rtmp://xxx.xxx.xxx.xxx/live

  png -> rtmp image

  2. About ffmpeg and named pipes, it seems to be written, and can not be read.

  # write
  
  .\ffmpeg.exe -i test.mp4 -f h264 pipe:MyPipe

  mp4 -> pipe image

  # read and push stream
  
  .\ffmpeg.exe -re -i pipe:MyPipe -vcodec libx264 -acodec aac -strict -2 -f h264 rtmp://xxx.xxx.xxx.xxx/live

  pipe -> rtmp image

  And ffmpeg official website does not seem to have an introduction about named pipes.

  Thank you for your help !

• How can I stream raw video frames AND audio to FFMPEG with Python 2.7 ?

  18 novembre 2017, par Just Askin

  I am streaming raw video frames from Pygame to FFMPEG, then sending to a rtmp stream, but for the life of me, I can’t figure out how to send live audio using the same Python module. It does not need to be the Pygame mixer, but I am not opposed to using it if that is where the best answer lies. I’m pretty sure it’s not though.

  My question is this : What is the best strategy to send live audio output from a program to FFMPEG along with raw video frames simultaneously from the same Python module ?

  My program is large, and eventually I would like to build options to switch audio inputs from a queue of music, a microphone, or any other random sounds from any program I want to use. But for the time being, I just want something to work. I am starting off with a simple Espeak command.

  Here is my Python commands :

  command = ['ffmpeg', '-re', '-framerate', '22', '-s', '1280x720', '-pix_fmt', 'rgba', '-f', 'rawvideo', '-i', '-', '-f', 's16le', '-ar', '22500', '-i', '/tmp/audio', '-preset', ultrafast', '-pix_fmt', 'rgba', '-b:v', '2500', '-s', 'hd720', '-r', '25', '-g', '50', '-crf', '20', '-f', 'flv', 'rtmp://xxx' ]
  
  
  
  pipe = sp.Popen(command, stdin=sp.PIPE) 

  Then I send my frames to stdin from within my main while True: loop.

  The problem I run into with this strategy is I can’t figure out how to shove audio into FFMPEG from within Python without blocking the pipe. After hours of research, I am pretty confident I can’t use the pipe to send the audio along with the frames. I thought the named pipe was my solution (which works running Espeak outside of Python), but it blocks Python until the Espeak is done... so no good.

  I assume I need threading for multiprocessing, but I cannot figure out from the official documentation or any other resources as to how I can solve my problem with it.

  The ['-f', 's16le', '-ar', '22500', '-i', '/tmp/audio'] are settings that work if I run espeak from a separate terminal with espeak 'some text' --stdout > /tmp/audio.

  I am using Centos 7, Python 2.7, pygame, the latest build of FFMPEG,

• OpenCV Alpha Channel support

  14 février 2014, par adriagil

  I've tried many different solutions but I'm stuck at this point.

  I have a sequence of .png files with alpha channel.
  If I pick one of the files for splitting the channels I got the expected result in an array[4] having the alpha channel

  Mat check = imread("1.png");

  printf("channels = %d", check.channels()); //got 'channels = 4'

  Then I expected to get the same results for a movie file.

  With FFMPEG I've just converted the .png sequence to a .mov file with "qtrle" codec that I'm sure that support alpha channel.

  ffmpeg -pix_fmt argb -i sequence_%d.png -vcodec qtrle output.mov

  Then the I process the video file frames with OpenCV

  Mat frame;
  
  VideoCapture cap ("output.mov");
  
  if (cap.grab())
  
      cap.retrieve(frame);
  
  printf("channels = %d", frame.channels()); // got 'channels = 3'

  I've checked the ffmpeg generated output and seems to be encoded right and have the alpha channel stored.

  Does OpenCV does not support Alpha Channel in movie files ?
  If so, anyone knows an alternative to do it with C++ or other libraries ?
  Can this be done with DirectX in some way (only using OpenCV for reading video) ?

  In the official docs I've found that cv::VideocCapture.retrieve() has a second argument for the 'channel' but I've tried to do the following with the same results (no alpha channel) :

  cap.retrieve(frame, 4);
  
  cap.retrieve(frame, -1);

  As far as cv::VideoCapture supports loading image sequences I've tried to load the PNG sequence but I got the following warning so I could not play the movie file :

  VideoCapture cap("sequence_%d.png");
  
  warning: Could not find codec parameters (../../modules/highgui/src/cap_ffmpeg_impl.hpp)

  Why I got that result if I can read the same PNG with imread("") ?

  Also I've tried to encode the .png sequence again with ffmpeg :

  ffmpeg -pix_fmt rgba -i sequence_%d.png -vcodec png output.mov

  But got exactly the same warning as before.

  Any suggestion would be much appreciated !

  Note : I'm using OpenCV 2.4.2 right now...maybe updating to 2.4.8 may solve the problem ?