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• avfilter/formats : Fix heap-buffer overflow when merging channel layouts

  13 août 2020, par Andreas Rheinhardt

  avfilter/formats : Fix heap-buffer overflow when merging channel layouts
  The channel layouts accepted by ff_merge_channel_layouts() are of two
  
  types : Ordinary channel layouts and generic channel layouts. These are
  
  layouts that match all layouts with a certain number of channels.
  
  Therefore parsing these channel layouts is not done in one go ; instead
  
  first the intersection of the ordinary layouts of the first input
  
  list of channel layouts with the ordinary layouts of the second list is
  
  determined, then the intersection of the ordinary layouts of the first
  
  one and the generic layouts of the second one etc. In order to mark the
  
  ordinary channel layouts that have already been matched as used they are
  
  zeroed. The inner loop that does this is as follows :
  for (j = 0 ; j < b->nb_channel_layouts ; j++) 
  
      if (a->channel_layouts[i] == b->channel_layouts[j]) 
  
          ret->channel_layouts[ret_nb++] = a->channel_layouts[i] ;
  
          a->channel_layouts[i] = b->channel_layouts[j] = 0 ;
  
      
  
  
  (Here ret->channel_layouts is the array containing the intersection of
  
  the two input arrays.)
  Yet the problem with this code is that after a match has been found, the
  
  loop continues the search with the new value a->channel_layouts[i].
  
  The intention of zeroing these elements was to make sure that elements
  
  already paired at this stage are ignored later. And while they are indeed
  
  ignored when pairing ordinary and generic channel layouts later, it has
  
  the exact opposite effect when pairing ordinary channel layouts.
  To see this consider the channel layouts A B C D E and E D C B A. In the
  
  first round, A and A will be paired and added to ret->channel_layouts.
  
  In the second round, the input arrays are 0 B C D E and E D C B 0.
  
  At first B and B will be matched and zeroed, but after doing so matching
  
  continues, but this time it will search for 0, which will match with the
  
  last entry of the second array. ret->channel_layouts now contains A B 0.
  
  In the third round, C 0 0 will be added to ret->channel_layouts etc.
  
  This gives a quadratic amount of elements, yet the amount of elements
  
  allocated for said array is only the sum of the sizes of a and b.
  This issue can e.g. be reproduced by
  
  ffmpeg -f lavfi -i anullsrc=cl=7.1 \
  
   af 'aformat=cl=mono|stereo|2.1|3.0|4.0,aformat=cl=4.0|3.0|2.1|stereo|mono' \
  
   f null -
  The fix is easy : break out of the inner loop after having found a match.
  Reviewed-by : Nicolas George <george@nsup.org>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavfilter/formats.c

• How can I use ffmpeg to create a seamless looping gif ? [closed]

  27 juin 2024, par DavidNyan10

  I have an MP4 file which contains animation repeating in a loop. Let's just say, for example, a video of rain. However, when loop is turned on, the video cuts off at the wrong place and does not make a nice smooth animation. The part where it loops is obvious. It's just that the video contains more than one cycle of the loop, but not an exact integer of the full cycle.

  


  My goal is to turn this video into a gif with a seamless loop. In other words, I want the last frame of the video to match the first frame.

  


  My approach : I found a "Seamless loop creator" website on Google, tried it out, and it worked REALLY well. I thought all my problems have been solved. But little did I know, I've been only looking at the few seconds at the beginning and at the end of the video, not paying attention to what's in the middle. The sneaky pesky little website cuts off the video right in the middle, stitch the "seamless transition" at the beginning and end of the video, and put an ugly cross-fade in the middle where the frames don't line up. That is stupid. This of course, isn't noticable on rain videos, but on videos like a character jumping, the crossfade is very visible.

  


  My second approach : I'd use FFMPEG to get the first frame of the video, then starting from the last frame of the video and backwards, it'd try to find a frame that matches exactly with the first frame.

  


  Steps :

  


  

  1. Get the first frame and save it as a PNG or something I don't know

  


  2. Reverse the original video

  


  3. Match the image to each frame of the video in step 2. It is now easier because it's not doing it backwards frame by frame.

  


  4. When a frame match is found, cut off all the frames before this matched frame.

  


  5. Reverse back the video

  


  


  Can I achieve something like this in ffmpeg, preferably a one-liner in windows cmd ?

  


  Follow-up question : Would it be better to leave the last frame the same as first frame or should I remove it ? For example, when it's looping, it would repeat that exact frame two times, is that good ? Or which one provides better results ? And if it's better to not include the last frame (the one that matches), how would I do it in my process above ?

  


  I tried ChatGPT, expecting a ready-made code. Put it in the command prompt and lost my original video file. Had to use a recovery tool because the file was overwritten.

  


• ffmpeg adts streaming with ezstream for icecast

  18 avril 2015, par Roberto Arosemena

  I’m trying to use ezstream to stream to an icecast server, my problem is while encoding the audio, I decode it from mp3 with madplay and I’m trying to encode it with ffmpeg so the output is aac, someone told me to use adts to be able to stream aac the problem is that the encoding doesn’t stream the audio, it shows the timer on the console but it goes from 0:00:00 to 0:00:40 to 0:01:30, etc until the song ends instead of going second by second, this is my config :

  <ezstream>
  
     <url>http://localhost:8100/t</url>
  
     <sourcepassword>password</sourcepassword>
  
     <format>MP3</format>
  
     <filename>/home/vybroo/server/audio/play.m3u</filename>
  
     <reencode>
  
        <enable>1</enable>
  
        <encdec>
  
           <format>MP3</format>
  
           <match>.mp3</match>
  
           <decode>madplay -b 16 -R 44100 -S -o raw:- @T@</decode>
  
           <encode>ffmpeg -f s16le -ar 44.1k -ac 2 -i - -b:a 32k -ar 44.1k -f adts -</encode>
  
        </encdec>
  
     </reencode>
  
  </ezstream>

  is the enconding config wrong ?, what should i change so it streams second by second correctly