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• How to convert from AV_PIX_FMT_BGRA to PIX_FMT_PAL8 ?

  29 juillet 2014, par Jona

  I’m having a hard time converting my images from AV_PIX_FMT_BGRA to PIX_FMT_PAL8. Unfortunately sws_getCachedContext doesn’t support the conversion to PIX_FMT_PAL8.

  What I’m trying to do is convert my images into a GIF video with higher quality output. It seems that PIX_FMT_PAL8 could potentially provide the higher quality output I’m looking for.

  According to this documentation I need to palettize the pixel data, but I have no clue how to do that.

  When the pixel format is palettized RGB (PIX_FMT_PAL8), the palettized
  image data is stored in AVFrame.data[0]. The palette is transported in
  AVFrame.data[1], is 1024 bytes long (256 4-byte entries) and is
  formatted the same as in PIX_FMT_RGB32 described above (i.e., it is
  also endian-specific). Note also that the individual RGB palette
  components stored in AVFrame.data[1] should be in the range 0..255.
  This is important as many custom PAL8 video codecs that were designed
  to run on the IBM VGA graphics adapter use 6-bit palette components.

  Any help or direction would be appreciated.

• Merge remote-tracking branch ’cehoyos/master’

  5 juillet 2014, par Michael Niedermayer

  Merge remote-tracking branch ’cehoyos/master’
  * cehoyos/master :
  
    Use os/2 palette even if it contains less than 256 entries.
  
    Assume that old bmps do not contain transparency information.
  
    Do not detect jp2 images as mov files.
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/bmp.c
  • [DH] libavformat/mov.c

• How to take screenshot (high fps) in Linux (programming)

  30 août 2014, par pirobtumen

  First of all I want to say that I’ve been reading a lot about this and I’ve learnt many ways to do it, but I haven’t been able to do it in linux.

  My project is an ambilight with arduino, so I need to take a screenshot of the desktop and analyze its colour.

  At the beginning I used Processing 2.0 with the class ’Robot’ from ’java.awt’. Initially I could take 5 frames per second and then I got 13fps. This works but I want more perfomance, so I start reading.

  In Windows or Mac you have libraries that let you access directly to the ’frameBuffer’, so you can take screenshot really ’easy’ and really fast.

  In Ubuntu I have tried python with Gtk, PIL, Qt... and the fastest way is GTK but I can only have about 15fps too.

  My problem is : I want to do it cross platform but I prefer that my program work in Linux at the beginning and then in Windows (I don’t like it too much :P).

  So, the first question : is python able to offer that perfomance ? Because I think that C++ can be a better option.

  And the second question : what do I need to do it ? I’ve read about Xlib (X11) but I can’t find documentation that let me take a screenshot. Also I know, for example, FFmpeg which is a powerful tool but I don’t know how to implement it.

  I hope that you could help me (and excuse me if I’ve made any mistakes).