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• Python 3 subprocess.popen() doesn't work on linux. Works on windows [closed]

  30 avril 2021, par user2628458

  process = subprocess.Popen(
    cmd, shell=True,
    stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
     universal_newlines=True)
for line in process.stdout:
    # ...


  


  I have this line that executes an FFmpeg job and throws out every line in the output to a variable. It works fine on Windows, but doesn't work at all on Linux. The for loop never gets executed. I can't find anything about this, or the difference between Windows and Linux subprocess.Popen(). Can you please point me the right way to fix this ?

  


• Python subprocesses (ffmpeg) only start once I Ctrl-C the program ?

  4 février 2016, par slhck

  I’m trying to run a few ffmpeg commands in parallel, using Cygwin and Python 2.7.

  This is roughly what I have :

  import subprocess
  
  processes = set()
  
  
  
  commands = ["ffmpeg -i input.mp4 output.avi", "ffmpeg -i input2.mp4 output2.avi"] 
  
  
  
  for cmd in commands:
  
    processes.add(
  
      subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
  
    )
  
  
  
  for process in processes:
  
    if process.poll() is None:
  
      process.wait()

  Now, once I am at the end of this code, the whole program waits. All the ffmpeg processes are created, but they’re idle, i.e., using 0% CPU. And the Python program just keeps waiting. Only when I hit Ctrl-C, it suddenly starts encoding.

  What am I doing wrong ? Do I have to "send" something to the processes to start them ?

• errors of 'vaGetDisplay' and `vaGetDisplayDRM' [duplicate]

  29 novembre 2018, par Kindermann

  This question already has an answer here :

  • errors when compiling c code with ffmpeg library
    
    1 answer
    

  After updating my ubuntu OS from 14.04 to 16.04, I installed the ffmpeg library using the following configurations :

  PATH="$HOME/bin:$PATH" PKG_CONFIG_PATH="$HOME/ffmpeg_build/lib/pkgconfig" ./configure \
  
    --prefix="$HOME/ffmpeg_build" \
  
    --pkg-config-flags="--static" \
  
    --extra-cflags="-I$HOME/ffmpeg_build/include" \
  
    --extra-ldflags="-L$HOME/ffmpeg_build/lib" \
  
    --bindir="$HOME/bin" \
  
    --enable-gpl \
  
    --enable-libass \
  
    --enable-libfdk-aac \
  
    --enable-libfreetype \
  
    --enable-libmp3lame \
  
    --enable-libopus \
  
    --enable-libtheora \
  
    --enable-libvorbis \
  
    --enable-libvpx \
  
    --enable-libx264 \
  
    --enable-nonfree
  
  PATH="$HOME/bin:$PATH" make
  
  make install

  It seemed to me the installation process was ok. After that, I tried to compile my own C source code with the following Makefile :

  EDITTED(adding -lva-drm -lva-x11 at line 10)

  FFMPEG_LIBS=    libavdevice                        \
  
                  libavformat                        \
  
                  libavfilter                        \
  
                  libavcodec                         \
  
                  libswresample                      \
  
                  libswscale                         \
  
                  libavutil                          \
  
  
  
  TARGET = video_analysis
  
  LIBS = -lva -lX11 -lvdpau -lm -lva-drm -lva-x11
  
  CC = gcc
  
  CFLAGS += -O2 -g -O0
  
  CFLAGS := $(shell pkg-config --cflags $(FFMPEG_LIBS)) $(CFLAGS)
  
  LDLIBS := $(shell pkg-config --libs $(FFMPEG_LIBS)) $(LDLIBS)
  
  
  
  .PHONY: default all clean
  
  
  
  default: $(TARGET)
  
  all: default
  
  
  
  OBJECTS = $(patsubst %.c, %.o, $(wildcard *.c))
  
  HEADERS = $(wildcard *.h)
  
  
  
  %.o: %.c $(HEADERS)
  
          $(CC) $(CFLAGS) -c $< -o $@
  
  
  
  .PRECIOUS: $(TARGET) $(OBJECTS)
  
  
  
  $(TARGET): $(OBJECTS)
  
      $(CC) $(OBJECTS) $(LDLIBS) $(LIBS) -o $@
  
  
  
  clean:
  
      -rm -f *.o
  
      -rm -f $(TARGET)

  However, my compiler complained the following errors :

  /root/ffmpeg_build/lib/libavutil.a(hwcontext_vaapi.o): In function `vaapi_device_create':
  
  /home/widerstand/ffmpeg_sources/ffmpeg/libavutil/hwcontext_vaapi.c:896: undefined reference to `vaGetDisplay'
  
  /home/widerstand/ffmpeg_sources/ffmpeg/libavutil/hwcontext_vaapi.c:917: undefined reference to `vaGetDisplayDRM'
  
  collect2: error: ld returned 1 exit status
  
  Makefile:30: recipe for target 'video_analysis' failed
  
  make: *** [video_analysis] Error 1

  My question is : in which library do ’vaGetDisplay’ and `vaGetDisplayDRM’ exist ? It’s for sure that libva functions properly. I have no clue how to fix the bugs...Thank you in advance !