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• Convert individual pixel values from RGB to YUV420 and save the frame - C++

  24 mars 2014, par learner

  I have been working with RGB->YUV420 conversion for sometime using the FFmpeg library. Already tried the sws_scale functionality but its not working well. Now, I have decided to convert each pixel individually, using colorspace conversion formulae. So, following is the code that gets me few frames and allows me to access individual R,G,B values of each pixel :

  // Read frames and save first five frames to disk
  
      i=0;
  
      while((av_read_frame(pFormatCtx, &packet)>=0) && (i<5)) 
  
      {
  
          // Is this a packet from the video stream?
  
          if(packet.stream_index==videoStreamIdx) 
  
          {   
  
              /// Decode video frame            
  
              avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
              // Did we get a video frame?
  
              if(frameFinished) 
  
              {
  
                  i++;
  
                  sws_scale(img_convert_ctx, (const uint8_t * const *)pFrame->data,
  
                            pFrame->linesize, 0, pCodecCtx->height,
  
                            pFrameRGB->data, pFrameRGB->linesize);
  
  
  
                  int x, y, R, G, B;
  
                  uint8_t *p = pFrameRGB->data[0];
  
                  for(y = 0; y < h; y++)
  
                  {  
  
                      for(x = 0; x < w; x++) 
  
                      {
  
                          R = *p++;
  
                          G = *p++;
  
                          B = *p++;
  
                          printf(" %d-%d-%d ",R,G,B);
  
                      }
  
                  }
  
  
  
                  SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);
  
              }
  
          }
  
  
  
          // Free the packet that was allocated by av_read_frame
  
          av_free_packet(&packet);
  
      }

  I read online that to convert RGB->YUV420 or vice-versa, one should first convert to YUV444 format. So, its like : RGB->YUV444->YUV420. How do I implement this in C++ ?

  Also, here is the SaveFrame() function used above. I guess this will also have to change a little since YUV420 stores data differently. How to take care of that ?

  void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame)
  
  {
  
      FILE *pFile;
  
      char szFilename[32];
  
      int  y;
  
  
  
      // Open file
  
      sprintf(szFilename, "frame%d.ppm", iFrame);
  
      pFile=fopen(szFilename, "wb");
  
      if(pFile==NULL)
  
          return;
  
  
  
      // Write header
  
      fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  
  
      // Write pixel data
  
      for(y=0; ydata[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  
  
      // Close file
  
      fclose(pFile);
  
  }

  Can somebody please suggest ? Many thanks !!!

• Paperclip with heroku and paperclip, migration fails

  2 décembre 2013, par jdartland

  I have a created ruby on rails application and I'm using paperclip to handle my file uploads.
  Paperclip works just fine on my local machine. But my video upload stops working when I deploy to Heroku. Does anyone know whats going wrong. I also get an error when I try to upload a video which says that the video filename does not exist. The photo upload works but not the Video, I'm using paperclip iwth nested attributes and ffmpeg.

  Upload Error log :

  Paperclip::Error (Asset model missing required attr_accessor for 'video_file_name')
  
  2013-12-02T14:38:16.867747+00:00 app[web.1]: Paperclip::Error (Asset model missing required attr_accessor for 'video_file_name'):
  
  2013-12-02T14:38:16.867747+00:00 app[web.1]:   app/controllers/projects_controller.rb:60:in `block in update'
  
  2013-12-02T14:38:16.867747+00:00 app[web.1]:   app/controllers/projects_controller.rb:59:in `update'

  Here is my migration error :

  Migrating to AddAttachmentPhotoToAssets (20131021134721)
  
  ==  AddAttachmentPhotoToAssets: migrating =====================================
  
  -- change_table(:assets)
  
     -> 0.0273s
  
  ==  AddAttachmentPhotoToAssets: migrated (0.0276s) ============================
  
  
  
  Migrating to AddProjectIdToAssets (20131022082744)
  
  -- add_column(:assets, :project_id, :integer)
  
  PG::DuplicateColumn: ERROR:  column "project_id" of relation "assets" already exists
  
  : ALTER TABLE "assets" ADD COLUMN "project_id" integer
  
  -- add_column(:assets, :project_id, :integer)
  
  PG::DuplicateColumn: ERROR:  column "project_id" of relation "assets" already exists
  
  : ALTER TABLE "assets" ADD COLUMN "project_id" integer
  
  rake aborted!
  
  PG::DuplicateColumn: ERROR:  column "project_id" of relation "assets" already exists
  
  : ALTER TABLE "assets" ADD COLUMN "project_id" integer
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in `exec'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in `block in execute'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:425:in `block in log'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:420:in `log'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:127:in `execute'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/schema_statements.rb:360:in `add_column'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/schema_statements.rb:379:in `add_column'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:625:in `block in method_missing'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:597:in `block in say_with_time'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:597:in `say_with_time'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:617:in `method_missing'
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:383:in `method_missing'
  
  /app/db/migrate/20131022082744_add_project_id_to_assets.rb:2:in `'
  
  /app/db/migrate/20131022082744_add_project_id_to_assets.rb:1:in `<top>&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:228:in `require&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:228:in `block in require&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:213:in `load_dependency&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:228:in `require&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:718:in `load_migration&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:714:in `migration&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:708:in `disable_ddl_transaction&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:1012:in `use_transaction?&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:922:in `rescue in block in migrate&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:919:in `block in migrate&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:916:in `each&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:916:in `migrate&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:764:in `up&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:742:in `migrate&#39;
  
  /app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/railties/databases.rake:42:in `block (2 levels) in <top>&#39;
  
  Tasks: TOP => db:migrate
  
  (See full trace by running task with --trace)
  
  </top></top>

  Here is my table :

   create_table "assets", force: true do |t|
  
      t.datetime "created_at"
  
      t.datetime "updated_at"
  
      t.string   "photo_file_name"
  
      t.string   "photo_content_type"
  
      t.integer  "photo_file_size"
  
      t.datetime "photo_updated_at"
  
      t.integer  "project_id"
  
      t.string   "video_file_name"
  
      t.string   "video_content_type"
  
      t.integer  "video_file_size"
  
      t.datetime "video_updated_at"
  
    end
  
  add_index "projects", ["permalink"], name: "index_projects_on_permalink", using: :btree
  
  
  
    create_table "settings", force: true do |t|
  
      t.string   "title"
  
      t.text     "description"
  
      t.text     "paragraph"
  
      t.datetime "created_at"
  
      t.datetime "updated_at"
  
      t.string   "photo_file_name"
  
      t.string   "photo_content_type"
  
      t.integer  "photo_file_size"
  
      t.datetime "photo_updated_at"
  
      t.string   "video_file_name"
  
      t.string   "video_content_type"
  
      t.integer  "video_file_size"
  
      t.datetime "video_updated_at"
  
    end

  Would gladly need some help ! :)

• ARM inline asm secrets

  6 juillet 2010, par Mans — ARM, Compilers

  Although I generally recommend against using GCC inline assembly, preferring instead pure assembly code in separate files, there are occasions where inline is the appropriate solution. Should one, at a time like this, turn to the GCC documentation for guidance, one must be prepared for a degree of disappointment. As it happens, much of the inline asm syntax is left entirely undocumented. This article attempts to fill in some of the blanks for the ARM target.
  

  Constraints

  Each operand of an inline asm block is described by a constraint string encoding the valid representations of the operand in the generated assembly. For example the “r” code denotes a general-purpose register. In addition to the standard constraints, ARM allows a number of special codes, only some of which are documented. The full list, including a brief description, is available in the constraints.md file in the GCC source tree. The following table is an extract from this file consisting of the codes which are meaningful in an inline asm block (a few are only useful in the machine description itself).

  f	Legacy FPA registers f0-f7.
  t	The VFP registers s0-s31.
  v	The Cirrus Maverick co-processor registers.
  w	The VFP registers d0-d15, or d0-d31 for VFPv3.
  x	The VFP registers d0-d7.
  y	The Intel iWMMX co-processor registers.
  z	The Intel iWMMX GR registers.
  l	In Thumb state the core registers r0-r7.
  h	In Thumb state the core registers r8-r15.
  j	A constant suitable for a MOVW instruction. (ARM/Thumb-2)
  b	Thumb only. The union of the low registers and the stack register.
  I	In ARM/Thumb-2 state a constant that can be used as an immediate value in a Data Processing instruction. In Thumb-1 state a constant in the range 0 to 255.
  J	In ARM/Thumb-2 state a constant in the range -4095 to 4095. In Thumb-1 state a constant in the range -255 to -1.
  K	In ARM/Thumb-2 state a constant that satisfies the I constraint if inverted. In Thumb-1 state a constant that satisfies the I constraint multiplied by any power of 2.
  L	In ARM/Thumb-2 state a constant that satisfies the I constraint if negated. In Thumb-1 state a constant in the range -7 to 7.
  M	In Thumb-1 state a constant that is a multiple of 4 in the range 0 to 1020.
  N	Thumb-1 state a constant in the range 0 to 31.
  O	In Thumb-1 state a constant that is a multiple of 4 in the range -508 to 508.
  Pa	In Thumb-1 state a constant in the range -510 to +510
  Pb	In Thumb-1 state a constant in the range -262 to +262
  Ps	In Thumb-2 state a constant in the range -255 to +255
  Pt	In Thumb-2 state a constant in the range -7 to +7
  G	In ARM/Thumb-2 state a valid FPA immediate constant.
  H	In ARM/Thumb-2 state a valid FPA immediate constant when negated.
  Da	In ARM/Thumb-2 state a const_int, const_double or const_vector that can be generated with two Data Processing insns.
  Db	In ARM/Thumb-2 state a const_int, const_double or const_vector that can be generated with three Data Processing insns.
  Dc	In ARM/Thumb-2 state a const_int, const_double or const_vector that can be generated with four Data Processing insns. This pattern is disabled if optimizing for space or when we have load-delay slots to fill.
  Dn	In ARM/Thumb-2 state a const_vector which can be loaded with a Neon vmov immediate instruction.
  Dl	In ARM/Thumb-2 state a const_vector which can be used with a Neon vorr or vbic instruction.
  DL	In ARM/Thumb-2 state a const_vector which can be used with a Neon vorn or vand instruction.
  Dv	In ARM/Thumb-2 state a const_double which can be used with a VFP fconsts instruction.
  Dy	In ARM/Thumb-2 state a const_double which can be used with a VFP fconstd instruction.
  Ut	In ARM/Thumb-2 state an address valid for loading/storing opaque structure types wider than TImode.
  Uv	In ARM/Thumb-2 state a valid VFP load/store address.
  Uy	In ARM/Thumb-2 state a valid iWMMX load/store address.
  Un	In ARM/Thumb-2 state a valid address for Neon doubleword vector load/store instructions.
  Um	In ARM/Thumb-2 state a valid address for Neon element and structure load/store instructions.
  Us	In ARM/Thumb-2 state a valid address for non-offset loads/stores of quad-word values in four ARM registers.
  Uq	In ARM state an address valid in ldrsb instructions.
  Q	In ARM/Thumb-2 state an address that is a single base register.

  Operand codes

  Within the text of an inline asm block, operands are referenced as %0, %1 etc. Register operands are printed as rN, memory operands as [rN, #offset], and so forth. In some situations, for example with operands occupying multiple registers, more detailed control of the output may be required, and once again, an undocumented feature comes to our rescue.

  Special code letters inserted between the % and the operand number alter the output from the default for each type of operand. The table below lists the more useful ones.

  c	An integer or symbol address without a preceding # sign
  B	Bitwise inverse of integer or symbol without a preceding #
  L	The low 16 bits of an immediate constant
  m	The base register of a memory operand
  M	A register range suitable for LDM/STM
  H	The highest-numbered register of a pair
  Q	The least significant register of a pair
  R	The most significant register of a pair
  P	A double-precision VFP register
  p	The high single-precision register of a VFP double-precision register
  q	A NEON quad register
  e	The low doubleword register of a NEON quad register
  f	The high doubleword register of a NEON quad register
  h	A range of VFP/NEON registers suitable for VLD1/VST1
  A	A memory operand for a VLD1/VST1 instruction
  y	S register as indexed D register, e.g. s5 becomes d2[1]