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• avcodec/cfhddata : Reduce stack usage

  3 septembre 2022, par Andreas Rheinhardt

  avcodec/cfhddata : Reduce stack usage
  Creating CFHD RL VLC tables works by first extending
  
  the codes by the sign, followed by creating a VLC,
  
  followed by deriving the RL VLC from this VLC (which
  
  is then discarded). Extending the codes uses stack arrays.
  The tables used to initialize the VLC are already sorted
  
  from left-to-right in the tree. This means that the
  
  corresponding VLC entries are generally also ascending,
  
  but not always : Entries from subtables always follow
  
  the corresponding main table although it is possible
  
  for the right-most node to fit into the main table.
  This suggests that one can try to use the final destination
  
  buffer as scratch buffer for the tables with sign included.
  
  Unfortunately it works for neither of the tables if one
  
  uses the right-most part of the RL VLC buffer as scratch buffer ;
  
  using the left-most part of the RL VLC buffer as scratch buffer
  
  might work if one traverses the VLC entries from end to start.
  
  But it works only for the little RL VLC (table 9), not for table 18.
  Therefore this patch uses the RL VLC buffer for table 9
  
  as scratch buffer for creating the bigger table 18.
  
  Afterwards the left part of the buffer for table 9 is
  
  used as scratch buffer to create table 9.
  This fixes the cfhd part of ticket #9399 (if it is not already fixed).
  
  Notice that I do not consider the previous stack usage excessive.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/cfhddata.c

• Vertically stack two images, draw a box on the bottom image then write multiline text in that box

  31 août 2020, par Sarmad S.

  I am trying to make a video from two images, where the two images should be vertically stacked. This is easy and can be done with the vstack command. I also managed to write text on the bottom image with the drawtext command. However I want to draw a blue box that covers half of the bottom image (the bottom part of the image) and write the text in that blue box.

  


  How do I go about doing so ?

  


  My code so far :

  


  ffmpeg -loop 1 -i image1 -i image2 -c:v libx264 -t 3 -pix_fmt yuv420p -filter_complex "[1]drawtext=my-font.otf: text='some multiline text': fontcolor=white: fontsize=50: x=(w-text_w)/2: y=(h-text_h)/2[v1], drawbox; [0][v1]vstack" -s 1080:1920 output.mp4"


  


  I also want to zoom slowly in the images (not the box or the text). Anyone can help me connect things ?

  


  I am able to zoom, drawbox, write text etc, but not able to combine them together.

  


• avformat/movenc : Fix stack overflow when remuxing timecode tracks

  30 septembre 2020, par Andreas Rheinhardt

  avformat/movenc : Fix stack overflow when remuxing timecode tracks
  There are two possible kinds of timecode tracks (with tag "tmcd") in the
  
  mov muxer : Tracks created internally by the muxer and timecode tracks
  
  sent by the user. If any of the latter exists, the former are
  
  deactivated. The former all belong to another track, the source
  
  track ; the latter don't have a source track set, but the index of the
  
  source track is initially zeroed by av_mallocz_array(). This is a
  
  problem since 3d894db700cc1e360a7a75ab9ac8bf67ac6670a3 : Said commit added
  
  a function that calculates the duration of tracks and the duration of
  
  timecode tracks is calculated by rescaling the duration (calculated by
  
  the very same function) of the source track. This gives an infinite
  
  recursion if the first track (the one that will be treated as source
  
  track for all timecode tracks) is a timecode track itself, leading to a
  
  stack overflow.
  This commit fixes this by not using the nonexistent source track
  
  when calculating the duration of timecode tracks not created internally
  
  by the mov muxer.
  Reviewed-by : Martin Storsjö <martin@martin.st>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/movenc.c