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• Python : Strange hanging behavior when piping large stdout of a subprocess

  7 septembre 2017, par Victor Odouard

  I am currently calling ffmpeg to extract a binary data stream from a video file, and then putting that binary data into a list. There is a lot of data in this data stream, about 4,000 kb. Here is the code

  # write and call ffmpeg command, piping stdout
  
  cmd = "ffmpeg -i video.mpg -map 0:1 -c copy -f data -"
  
  proc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
  
  
  
  # read from stdout, byte by byte
  
  li = []
  
  for char in iter(lambda: proc.stdout.read(1), ""):
  
      li.append(char)

  This works fine. However, if I take out the part where I am reading from stdout, it starts working but then hangs :

  cmd = "ffmpeg -i video.mpg -map 0:1 -c copy -f data -"
  
  proc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
  
  time.sleep(10)

  I had to add time.sleep(10) at the end or else the process would end before the subprocess, causing this error :

  av_interleaved_write_frame(): Invalid argument
  
  Error writing trailer of pipe:: Invalid argument
  
  size=       0kB time=00:00:00.00 bitrate=N/A speed=N/A
  
  video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing ove
  
  rhead: 0.000000%
  
  Conversion failed!

  Calling either subprocess.call(cmd, stdout=subprocess.PIPE) or subprocess.call(cmd) also cause hanging (the latter just displays the stdout in the console while the former doesn’t).

  Is there something about reading from stdout that prevents this hanging (like perhaps the buffer getting cleared), or am I unknowingly introducing a bug elsewhere ? I’m worried that such a small change causes the program to break ; it doesn’t inspire very much confidence.

  The other issue with this code is that I need to read from the list from another thread. This might mean I need to use a Queue. But when I execute the below code, it takes 11 seconds as opposed to 3 seconds with the list equivalent :

  cmd = "ffmpeg -i video.mpg -loglevel panic -hide_banner -map 0:1 -c copy -f data -"
  
  proc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
  
  
  
  q = Queue()
  
  
  
  for char in iter(lambda: proc.stdout.read(1), ""):
  
      q.put(char)

  Should I be using another data structure ?

• h264_sei : Add namespace prefix to all SEI values

  15 mai 2017, par Mark Thompson

  h264_sei : Add namespace prefix to all SEI values
  This avoids confusion with equivalent H.265 SEI values when both are
  
  being used at the same time.
  (cherry picked from commit 6ea220cbeec8863e2006a03b73bed52db2b13ee7)
  

  • [DH] libavcodec/h264_parser.c
  • [DH] libavcodec/h264_sei.c
  • [DH] libavcodec/h264_sei.h
  • [DH] libavcodec/h264_slice.c
  • [DH] libavcodec/vaapi_encode_h264.c
  • [DH] libavcodec/videotoolboxenc.c

• avcodec/frame_thread_encoder : Fix AV_OPT_TYPE_STRING handling in avctx

  13 septembre 2017, par Reimar Döffinger

  avcodec/frame_thread_encoder : Fix AV_OPT_TYPE_STRING handling in avctx
  This is the equivalent to what 7d317d4706b49d572a1eb5269438753be18362c7
  
  did for the codec-specific options.
  
  av_opt_copy has specific handling so it's fine that we already copied
  
  the whole context before.
  Signed-off-by : Reimar Döffinger <Reimar.Doeffinger@gmx.de>
  

  • [DH] libavcodec/frame_thread_encoder.c