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• How do dcraw and stdin work together ?

  25 juillet 2018, par Metin Akkın

  I want to use this :

  dcraw -a -q 3 -6 -v -I < a.nef

  but the picture becomes a dark image. I changed draw.c library but it doesnt work. I want to use stdin and I use this link : https://blog.mclemon.io/dcraw-and-stdin. Please help me.

• Convert static file to h264 stream with FFmpeg [on hold]

  28 août 2013, par Vprnl

  I'm building a NodeJS application that converts a static videofile to a streamable video which is being sent to a client (iPad or browser) on the fly (using the fluent-ffmpeg module).

  Everything is set and all I need now is to configure ffmpeg correctly. But I'm having a lot of problems with ffmpeg.

  With my current settings, I hear audio right away, but the picture starts a couple of seconds later. Then, my 30 second test file has been compressed to 3 seconds of high speed imagery.

  How can I configure my ffmpeg so it will stream the mp4 correctly (in one pass through of course). It seems it is streaming raw h264, if that is the case how can I force the mp4 container. I thought I was doing that by using '-f mp4'

  my correct settings are :

     '-crf 22','-c:v libx264','-f mp4','-movflags','faststart+frag_keyframe'

  I've also tried :

   '-r 30','-crf 30','-analyzeduration 0','-probesize 1000','-rc_lookahead 0','-fflags nobuffer','-g 75','-ss 0','-threads 0','-vcodec libx264','-qcomp 0.6','-qmin 10','-qmax 51','-qdiff 4','-b:v 400k','-maxrate 400k','-bufsize 800k','-acodec mp3','-ab 192k','-ar 44100','-tune zerolatency','-f mp4','-movflags','faststart+frag_keyframe'

  As you can see by the amount of options I've tried, I'm getting pretty desperate. I'm basically just running around in the dark.

  I don't think it matters much but these are my request headers :

                      res.writeHead(200, { // NOTE: a partial http response
  
                          'Content-Type':'video/mp4',
  
                          'Content-Length':stat.size,
  
                          'Content-Range':'bytes '+start+'-'+end+'/'+stat.size,
  
                          'Transfer-Encoding':'chunked'
  
                      });

• More Weird VP8 Encodings

  10 décembre 2010, par Multimedia Mike — VP8

  When I announced that I had transitioned my VP8 encoder’s status from "toy" to "working", Jim L. lamented the loss of humorous posts about oddly encoded images output from my encoder. Not so ! There are still plenty of features that I have yet to implement, each of which carries the possibility of bizarre images.

  For example, I dusted off my work-in-progress intra 4x4 encoding, fixed a few of the more obvious bugs, and told the encoder to encode the first block in 4x4 mode and the rest in the usual, working, debugged 16x16 mode. The results of the first pass surprised me :

  
  
  

  The reason this surprised me was that I intuitively expected one of 2 outcomes :

  • Perfect image right away since everything is correct (very unlikely but not outside the realm of possibility)
  • Total garbage with, at most, the first macroblock looking somewhat legible ; this would be due to having some of the first macroblock correct but completely desynchronizing the bitstream for the purpose of decoding the rest of the coefficients.

  I absolutely did not expect the first macroblock to look messed up but for the rest of the picture to look fine. For fun, I reversed the logic and encoded the first block as 16x16 and the rest with the experimental 4x4 mode :

  
  
  

  If you examine carefully, you will see that the color planes are correct (though faint). There just isn’t much going on in the luma plane. This made sense when I noticed the encoder was encoding a blank (undefined, actually) set of luma coefficients for 4x4 mode macroblocks due to a bug. This helps to rationalize the first image as well— the first macroblock was encoding nonsense for the first macroblock which messed up the macroblocks which immediately surrounded it. Eventually, macroblock decoding got back on track when the prediction modes weren’t relying on the errantly decoded macroblocks.

  After I fixed that bug, I let the 4x4 mode rip through the whole image. That’s when I got what I am terming the "dark and gritty reboot of Big Buck Bunny" :

  
  
  

  Fortunately, this also turned out to be traceable to a pretty obvious code bug.

  One day, this VP8 encoder might do the right thing while implementing all of the algorithm’s features. In the meantime, it’s at least entertaining to watch it make mistakes.