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• Anomalie #2448 (Résolu) : affectation de variables directement depuis la query-string sans filtrag...

  9 décembre 2011, par cy_altern -

  à priori réglé avec http://zone.spip.org/trac/spip-zone/changeset/55304

• avdevice/decklink_enc : use 64bit format string for BMD timebase instead of long long

  2 juillet 2023, par Marton Balint

  avdevice/decklink_enc : use 64bit format string for BMD timebase instead of long long
  BMDTimeValue is defined as LONGLONG on Windows, but int64_t on Linux/Mac.
  Fixes format string warnings :
  libavdevice/decklink_enc.cpp : In function ‘void construct_cc(AVFormatContext*, decklink_ctx*, AVPacket*, klvanc_line_set_s*)’ :
  
  libavdevice/decklink_enc.cpp:424:48 : warning : format ‘%lld’ expects argument of type ‘long long int’, but argument 4 has type ‘BMDTimeValue aka long int’ [-Wformat=]
  
                  ctx->bmd_tb_num, ctx->bmd_tb_den) ;
  
   ^
  
  libavdevice/decklink_enc.cpp:424:48 : warning : format ‘%lld’ expects argument of type ‘long long int’, but argument 5 has type ‘BMDTimeValue aka long int’ [-Wformat=]
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavdevice/decklink_enc.cpp

• Convert an h264 byte string to OpenCV images

  27 novembre 2017, par Fred Dufresne

  In Python, how do I convert an h264 byte string to images OpenCV can read, only keeping the latest image ?

  Long version :

  Hi everyone.

  Working in Python, I’m trying to get the output from adb screenrecord piped in a way that allows me to capture a frame whenever I need it and use it with OpenCV. As I understand, I need to constantly read the stream because it’s h264.

  I’ve tried multiple things to get it working and concluded that I needed to ask for specific help.

  The following gets me the stream I need and works very well when I print stream.stdout.read(n).

  import subprocess as sp
  
  
  
  adbCmd = ['adb', 'exec-out', 'screenrecord', '--output-format=h264', '-']
  
  stream = sp.Popen(adbCmd, stdout = sp.PIPE, universal_newlines = True)

  Universal newlines was necessary to get it to work on Windows.

  Doing :

  sp.call(['ffplay', '-'], stdin = stream.stdout, universal_newlines = True)

  Works.

  The problem is I am now trying to use ffmpeg to take the input h264 stream and output as many frames as possible, overwriting the last frame if needed.

  ffmpegCmd = ['ffmpeg', '-f', 'image2pipe', '-pix_fmt', 'bgr24', '-vcodec', 'h264', 'fps=30', '-']
  
  ffmpeg = sp.Popen(ffmpegCmd, stdin = stream.stdout, stdout = sp.PIPE, universal_newlines = True)

  This is what I think should be used, but I always get the error "Output file #0 does not contain any stream".

  Edit :

  Final Answer

  Turns out the universal_newlines option was ruining the line endings and gradually corrupting the output. Also, the ffmpeg command was wrong, see LordNeckbeard’s answer.

  Here’s the correct ffmpeg command to achieve what was used :

  ffmpegCmd = ['ffmpeg', '-i', '-', '-f', 'rawvideo', '-vcodec', 'bmp', '-vf', 'fps=5', '-']
  
  ffmpeg = sp.Popen(ffmpegCmd, stdin = stream.stdout, stdout = sp.PIPE)

  And then to convert the result into an OpenCV image, you do the following :

  fileSizeBytes = ffmpeg.stdout.read(6)
  
  fileSize = 0
  
  for i in xrange(4):
  
      fileSize += fileSizeBytes[i + 2] * 256 ** i
  
  bmpData = fileSizeBytes + ffmpeg.stdout.read(fileSize - 6)
  
  image = cv2.imdecode(np.fromstring(bmpData, dtype = np.uint8), 1)

  This will get every single frame of a stream as an OpenCV image.