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• How to set timestamps when concat with ffmpeg ?

  27 avril 2020, par doner

  Suppose I concatenate 2 clips :

  



  ffmpeg -f concat -i input.txt -c copy output.mp4


  



  The first clip has 7 frames 60 fps :

  



  0.000000,0
0.016667,0
0.033333,0
0.050000,0
0.066667,0
0.083333,0
0.100000,0


  



  The second clip has 4 frames 60 fps :

  



  0.116667,0
0.133333,0
0.150000,0
0.166667,0


  



  Can I set the "distance" between concatenated clip (between the last frame of the previous clip and the first frame of the next clip) ? In the example above the difference 0.116667 - 0.100000 = 0.016667. If I'd like to set 0.02 instead of 0.016667 how can I do that ?

  


• Set aria-invalid attribute based on validation

  7 octobre 2013, par nschonni

  Set aria-invalid attribute based on validation
  As per http://www.w3.org/TR/wai-aria/states_and_properties#aria-invalid
  
  the validation states should only be added after a user has had a chance
  
  to enter a value
  

• Giving Thanks For VP8

  25 novembre 2010, par Multimedia Mike — VP8

  It’s the Thanksgiving holiday here in the United States. I guess that’s as good a reason as any to release a first cut of my VP8 encoder. In order to remind people that they shouldn’t expect phenomenal quality from it — and to discourage inexperienced people from trying to create useful videos with it — I have hardcoded the quantizers to their maximum settings. For those not skilled in the art, this is the setting that yields maximum compression and worst quality. When compressing the Big Buck Bunny logo image, the resulting file is only 2839 bytes but observe the reconstructed quality :

  
  
  It really just looks like a particularly stormy day in the forest.
  

  First VP8 File From An Independent Encoder
  I found a happy medium on the quantizer scale and encoded the first 30 seconds of Big Buck Bunny for your inspection. I guess this makes it the first VP8/WebM file from an independent encoder (using FFmpeg’s Matroska muxer as well).

  Download : bbb-360p-30sec-q40.webm ( 13 MBytes)

  I think the quality makes it look like it was digitized from an old VHS tape.

  For fun, here’s the version with the quantizer cranked to the max : bbb-360p-30sec-q127.webm ( 1.3 MBytes)

  Aside : I was going to encapsulate the video in this post using a bare HTML5 <video> tag for the benefit of the small browsing population who could view that (indeed, it works fine in Chrome). But that would be insane due to the fact that supporting browsers preload the video with no easy (read : without the help of JavaScript) method for overriding this unacceptable default.

  The Code
  I’m still trying to get over my fear of git. To that end, I have posted the code on Github :

  https://github.com/multimediamike/ffvp8enc

  I still don’t like you, git. But I’m sure we’ll find some way to make this work.

  Other required code changes in the basic FFmpeg tree :

  • Of course, copy vp8enc.c into libavcodec/
  • In libavcodec/allcodecs.c, ’REGISTER_DECODER (VP8, vp8);’ turns into ’REGISTER_ENCDEC (VP8, vp8);’
  • Add ’OBJS-$(CONFIG_VP8_ENCODER) += vp8enc.o’ to libavcodec/Makefile

  Further Work
  About the limitations and work yet to do :

  • it’s still intra-only, no interframes (which is where a lot of compression occurs)
  • no rate control or distortion optimization, obviously
  • no intra 4x4 coding (that’s close to working but didn’t my little T-day deadline)
  • no quantization control ; this should really be hooked up to the FFmpeg command line but I’m not sure how
  • encoder writes into a static-sized, 1/2 MB memory buffer ; this can overflow
  • code is a mess (what did you expect at this stage of the game ?)
  • lots and lots of other things, surely