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• avcodec/htmlsubtitles : Check for string truncation and return error

  5 mai 2017, par Michael Niedermayer

  avcodec/htmlsubtitles : Check for string truncation and return error
  Fixes out of array access
  
  Fixes : 1354/clusterfuzz-testcase-minimized-5520132195483648
  Found-by : continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/htmlsubtitles.c
  • [DH] libavcodec/htmlsubtitles.h

• webm_dash_manifest_demuxer : Fix UB in cue timestamp string code and make it actually...

  20 avril 2017, par Derek Buitenhuis

  webm_dash_manifest_demuxer : Fix UB in cue timestamp string code and make it actually work
  Output was apparently not tested for correctness. Passing overlapping
  
  memory to snprintf causes undefined behavior, and usually resulted in
  
  only the very last timestamp being written to metadata, and not a list
  
  at all.
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DH] libavformat/matroskadec.c

• Convert an h264 byte string to OpenCV images

  24 mars 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.