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• Cortex-A7 instruction cycle timings

  15 mai 2014, par Mans — ARM

  The Cortex-A7 ARM core is a popular choice in low-power and low-cost designs. Unfortunately, the public TRM does not include instruction timing information. It does reveal that execution is in-order which makes measuring the throughput and latency for individual instructions relatively straight-forward. The table below lists the measured issue cycles … Continue reading →

• Programmatically get non-overlapping images from MP4

  16 novembre 2019, par Carlos F

  My ultimate goal is to get meaningful snapshots from MP4 videos that are either 30 min or 1 hour long. "Meaningful" is a bit ambitious, so I have simplified my requirements.

  The image should be crisp - non-overlapping, and ideally not blurry. Initially, I thought getting a keyframe would work, but I had no idea that keyframes could have overlapping images embedded in them like this :

  Of course, some keyframe images look like this and those are much better :

  

  I was wondering if someone might have source code to :

  Take a sequence of say 10-15 continuous keyframes (jpg or png) and identify the best keyframe from all of them.

  This must happen entirely programmatically. I found this paper : http://research.microsoft.com/pubs/68802/blur_determination_compressed.pdf

  and felt that I could "rank" a few images based on the above paper, but then I was dissuaded by this link : Extracting DCT coefficients from encoded images and video given that my source video is an MP4. Of course, this confuses me because the input into the system is just a sequence of jpg images.

  Another link that is interesting is :

  Detection of Blur in Images/Video sequences

  However, I am not sure if this will work for "overlapping" images.

• avutil/file_open : avoid file handle inheritance on Windows

  29 octobre 2015, par Tobias Rapp

  avutil/file_open : avoid file handle inheritance on Windows
  Avoids inheritance of file handles on Windows systems similar to the
  
  O_CLOEXEC/FD_CLOEXEC flag on Linux.
  Fixes file lock issues in Windows applications when a child process
  
  is started with handle inheritance enabled (standard input/output
  
  redirection) while a FFmpeg transcoding is running in the parent
  
  process.
  Links relevant to the subject :
  https://msdn.microsoft.com/en-us/library/w7sa2b22.aspx
  Describes the _wsopen() function and the O_NOINHERIT flag. File handles
  
  opened by _wsopen() are inheritable by default.
  https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425%28v=vs.85%29.aspx
  Describes handle inheritance when creating new processes. Handle
  
  inheritance must be enabled (bInheritHandles = TRUE) e.g. when you want
  
  to pass handles for stdin/stdout via lpStartupInfo.
  Signed-off-by : Tobias Rapp <t.rapp@noa-audio.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavutil/file_open.c