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• ffmpeg fast accurate cut

  28 July 2019, by Ali Rasooli

  I want to cut a part of Video file without re-encoding whole video.
  This is the method came to my mind:

  

  first.mp4:

  ffmpeg -i in.mp4 -ss start_cut -t start_to_a first.mp4

  last.mp4:

  ffmpeg -i in.mp4 -ss b -t b_to_end last.mp4

  middle.mp4

  ffmpeg -i in.mp4 -ss a -t a_to_b -c copy middle.mp4

  then merge these three files with:

  merge -f concat -i fileslist -c copy out.mp4

  I tested this method but it’s not giving expected output the 3 video files are cut ok but after merging the middle part slows down and has low quality in out.mp4.

  What is the problem with this method? Or is there another method to fast accurate cut?

  Thank you.

• Revision df037b615f: Adding API to read/write uncompressed frame header bits. The API is not final y

  22 May 2013, by Dmitry Kovalev

  Changed Paths:
   Modify /vp9/common/vp9_common.h

  
   Delete /vp9/common/vp9_header.h

  
   Modify /vp9/common/vp9_onyxc_int.h

  
   Modify /vp9/decoder/vp9_decodframe.c

  
   Add /vp9/decoder/vp9_read_bit_buffer.h

  
   Modify /vp9/encoder/vp9_bitstream.c

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Add /vp9/encoder/vp9_write_bit_buffer.h

  
   Modify /vp9/vp9_common.mk

  
   Modify /vp9/vp9_dx_iface.c

  
   Modify /vp9/vp9cx.mk

  
   Modify /vp9/vp9dx.mk

  
  
  Adding API to read/write uncompressed frame header bits.

  The API is not final yet and can be changed. Actual layout of
  uncompressed frame part will be finalized later. Right now moving
  clr_type, error_resilient_mode, refresh_frame_context,
  frame_parallel_decoding_mode from first compressed partition to
  uncompressed frame part.

  Change-Id: I3afc5d4ea92c5a114f4c3d88f96858cccc15b76e

• yuv to rgb conversion using OpenGL ES2.0 in android,

  8 October 2013, by 101110101100111111101101

  I have 2 questions about yuv to rgb conversion using OpenGL ES2.0 in android.

  First thing needs little background.

  -------BACK GROUND------

  When I put random data(YUVs one), It renders like good. (I'm not certain because data is
  random data.)

  however, When I put 'real' one, that is awkaward, important is 'render something'.

  I checked my codes(renderer, data parser, etc... every where), and no doubtful part , except for using GL_RGB parameters in method 'glRenderbufferStorage', 'glTexImage2D'...

  I changed that parameters many times which is in 'glRenderbufferStorage'(GL_RGBA4, GL_RGB565 etc... ). (current is GL_RGBA4)

  but no changed. (some parameters occur error, no rendering.)

  and 'glTexImage2D's parameters too. (current is GL_LUMINANCE.)

  Before Conversion : YUV420P (from ffmpeg pix_fmt_YUV420p) (16bpp, 2X2 Y4 Cb1 Cr1)
  After Conversion : RGB. (I don't know what's difference with RGB series... RGBA, RGB565 etc)
  Before decodedData : decoded linesize is 736 height is 480. (fixed)

  so 12*736*480/8 -> array size;
  Y is 736 * 480
  U is arraysize * 1/4;
  V is arraysize * 1/4;

  ---------BACK GROUND END-----------

  I wondering GL_RGB or RGBA4 or RGB565 that parameters effect output data's result?
  Not part of quality, but part of rendering or not.

  Second part is about fragment shader.

  My rendering engine structure has 3texture in fragment shader. (attach source below)

          "precision mediump float;               \n"
  
      "varying vec2 v_vTexCoord;          \n"
  
      "uniform sampler2D yTexture;        \n"
  
      "uniform sampler2D uTexture;        \n"
  
      "uniform sampler2D vTexture;        \n"
  
      "void main() {                      \n"
  
          "float y=texture2D(yTexture, v_vTexCoord).r;\n"
  
          "float u=texture2D(uTexture, v_vTexCoord).r;\n"
  
          "float v=texture2D(vTexture, v_vTexCoord).r;\n"
  
          "y=1.1643 * (y - 0.0625);\n"
  
          "u=u - 0.5;\n"
  
          "v=v - 0.5;\n"
  
          "float r=y + 1.5958 * v;\n"
  
          "float g=y - 0.39173 * u - 0.81290 * v;\n"
  
          "float b=y + 2.017 * u;\n"
  
          "gl_FragColor = vec4(r, g, b, 1.0);\n"
  
      "}\n";

  as you know, there are three texture, Ytex,Utex,Vtex.
  and then, it converts, and gl_FragColor = vec4(r,g,b,1.0);
  I don't know gl_FragColor = vec4(r,g,b,1.0) means.
  of cource, I know gl_FragColor is set, but How can I get actual r,g,b value?
  it renders in texture automatically?