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• x86 : SSE2/AVX idct_dequant_2x4_(dc|dconly)

  20 février 2016, par Henrik Gramner

  x86 : SSE2/AVX idct_dequant_2x4_(dc|dconly)
  Only used in 4:2:2. Both 8-bit and high bit-depth implemented.
  Approximate performance improvement compared to C on Ivy Bridge :
                           x86-32  x86-64
  
  idct_dequant_2x4_dc      2.1x    1.7x
  
  idct_dequant_2x4_dconly  2.7x    2.0x
  Helps more on 32-bit due to the C versions being register starved.
  

  • [DH] common/quant.c
  • [DH] common/x86/quant-a.asm
  • [DH] common/x86/quant.h

• How to read YUV8 data from avi file ?

  3 septembre 2013, par Srv19

  I have avi file that contains uncompressed gray video data. I need to extract frames from it. The size of file is 22 Gb.

  How do i do that ?

  I have already tried ffmpeg, but it gives me "could not find codec parameters for video stream" message - because there is no codec at work, just frames.

  Since Opencv just uses ffmpeg to read video, that rules out opencv as well.

  The only path that seems to be left is to try and dig into the raw data, but i do not know how.

  Edit : this is the code i use to read from the file with opencv. The failure occurs inside the second if. Running ffmpeg binary on the file also fails with the message above (could not find codec aprameters etc)

  /* register all formats and codecs */
  
  av_register_all();
  
  
  
  /* open input file, and allocate format context */
  
  if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
  
      fprintf(stderr, "Could not open source file %s\n", src_filename);
  
      ret = 1;
  
      goto end;
  
  }
  
  fmt_ctx->seek2any = true;
  
  /* retrieve stream information */
  
  int res = avformat_find_stream_info(fmt_ctx, NULL);
  
  if (res < 0) {
  
      fprintf(stderr, "Could not find stream information\n");
  
      ret = 1;
  
      goto end;
  
  }

  Edit :

  Here is sample code i have tried to make the extraction : pastebin. The result i get is an unchanging buffer after every call to AVIStreamRead.

• Rails MP4 playback working in Chrome but not Firefox

  9 février 2015, par Mark Boulder

  I got these MP4 video uploads via Paperclip that play just fine in Chrome but not in Firefox. Anybody know why that is ?

  http://runnable.com/VNkNeJ9wpNZJBEma/paperclip-mp4-problem

  Click Run and navigate to the last post to see the MP4. If you get a something bad happened from Runnable just try reloading the page.

  I tried adding Mime::Type.register "video/mp4", :mp4 to config/initializers/mime_types.rb but to no avail.

  • http://caniuse.com/#feat=video
  • Rails : MIME type issues with .m4v files
  • HTML5 video (mp4 and ogv) problems in Safari and Firefox - but Chrome is all good