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• Understanding the VP8 Token Tree

  7 juin 2010, par Multimedia Mike — VP8

  I got tripped up on another part of the VP8 decoding process today. So I drew a picture to help myself understand it. Then I went back and read David Conrad’s comment on my last post regarding my difficulty understanding the VP8 spec and saw that he ran into the same problem. Since we both experienced the same hindrance in trying to sort out this matter, I thought I may as well publish the picture I drew.

  VP8 defines various trees for decoding different syntax elements. There is one tree for decoding the tokens and it is expressed in the VP8 spec as such :

  PLAIN TEXT

  C :

  1. const tree_index coef_tree [2 * (num_dct_tokens - 1)] =
  2. {
  3.  -dct_eob, 2,        /* eob = "0"  */
  4.   -DCT_0, 4,        /* 0  = "10" */
  5.   -DCT_1, 6,        /* 1  = "110" */
  6.    8, 12,
  7.    -DCT_2, 10,      /* 2  = "11100" */
  8.     -DCT_3, -DCT_4,    /* 3  = "111010", 4 = "111011" */
  9.    14, 16,
  10.     -dct_cat1, -dct_cat2, /* cat1 = "111100", cat2 = "111101" */
  11.    18, 20,
  12.     -dct_cat3, -dct_cat4, /* cat3 = "1111100", cat4 = "1111101" */
  13.     -dct_cat5, -dct_cat6 /* cat4 = "1111110", cat4 = "1111111" */
  14. } ;

  Here is what the table looks like when you make a tree out of it (click for full size image) :

  
  
  

  The catch is that it makes no sense for an end-of-block (EOB) token to follow a 0 token since EOB already indicates that the remainder of the coefficients should be 0 anyway. Thus, the spec states that, "decoding of certain DCT coefficients may skip the first branch, whose preceding coefficient is a DCT_0." I confess, I didn’t understand what "skip the first branch" meant until I drew the tree.

  
  
  

  For those wondering why it might be sub-optimal (clarity-wise) for a spec to simply regurgitate vast chunks of C code, this makes a decent case. As you can see, the spec makes certain assumptions about how a binary tree should be organized in a static array (node n points to elements n*2 and n*2+1 as its branches ; leaves are either negative or 0). This is the second method I have seen ; another piece of code (not the VP8 spec) had the nodes in the first half of the array and pointed to leaves in the second half. There must be other arrangements.

• Use Google Fonts In ffmpeg fontfile

  9 mars 2020, par Randy Thomas

  I am wanting to use Google Fonts in my ffmpeg video creations for text. Here is what I have and it’s not working at all.

  $font = "//fonts.googleapis.com/css?family=Aclonica";
  
  
  
  $cmd .= "drawtext=enable='between(t,".$fi.",".$li.")':fontfile=".$font.":fontsize=".$fontsize.":fontcolor=".$color.":x=(w-text_w)/2:y=(h/2)+".$n.":text='".$arr[$j]."',";

  Of course, this works with .ttf fonts but I really want to use Google Fonts.

  I have also tried $font = "https://fonts.googleapis.com/css?family=Aclonica" that does not work either.

  I have a feeling that ffmpeg does not use woff2 fonts but I have seen a site that does this I just can’t say 100% for sure that they use Google Fonts in the creation, but they do use them in the selection of the font which leads me to believe they use them in the creation of the video.

• Mac app crash : Termination Reason : Namespace CODESIGNING, Code 0x2 [closed]

  29 janvier 2020, par dummyapps

  The app always works fine, but it suddenly crashes this evening and report "Namespace CODESIGNING, Code 0x2", I have no idea why, the code worked for several year, it seems that certain certificate invalid.

  This app use FFmpeg library to snapshot video, I did some test on it :

  1. I rebuild the source code, It still crash.

  2. It only crash on Mac OS 10.15, it works fine on 10.13

  3. I use atos to analyse the crash report, the output of atos indicate that FFmpeg library failed, but it should not. The code works for several year, I don’t think the code has bug.

  4. I submit a Technical Support to Apple developer, they also have no idea why.

     System Integrity Protection : enabled

     Crashed Thread : 3 Dispatch queue : com.dummyapps.videoBrowser.screenshot

     Exception Type : EXC_BAD_ACCESS (Code Signature Invalid)
     Exception Codes : 0x0000000000000032, 0x00000001134b5000
     Exception Note : EXC_CORPSE_NOTIFY

     Termination Reason : Namespace CODESIGNING, Code 0x2

     kernel messages :

     VM Regions Near 0x1134b5000 :
     CoreAnimation 00000001134ac000-00000001134b2000 [ 24K] rw-/rwx SM=PRV
     
     — > VM_ALLOCATE 00000001134b5000-00000001134b6000 [ 4K] r-x/rwx SM=PRV
     CoreAnimation 00000001134b6000-00000001134ba000 [ 16K] rw-/rwx SM=PRV

     Thread 0: : Dispatch queue : com.apple.main-thread
     0 libsystem_kernel.dylib 0x00007fff69f8625a mach_msg_trap + 10
     1 libsystem_kernel.dylib 0x00007fff69f865d0 mach_msg + 60
     2 com.apple.CoreFoundation 0x00007fff327ead0b __CFRunLoopServiceMachPort + 322
     3 com.apple.CoreFoundation 0x00007fff327e98e7 __CFRunLoopRun + 1695
     4 com.apple.CoreFoundation 0x00007fff327e8bd3 CFRunLoopRunSpecific + 499
     5 com.apple.HIToolbox 0x00007fff3133f65d RunCurrentEventLoopInMode + 292
     6 com.apple.HIToolbox 0x00007fff3133f39d ReceiveNextEventCommon + 600
     7 com.apple.HIToolbox 0x00007fff3133f127 _BlockUntilNextEventMatchingListInModeWithFilter + 64
     8 com.apple.AppKit 0x00007fff2f9b0eb4 _DPSNextEvent + 990
     9 com.apple.AppKit 0x00007fff2f9af690 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue :] + 1352
     10 com.apple.AppKit 0x00007fff2f9a13ae -[NSApplication run] + 658
     11 com.apple.AppKit 0x00007fff2f973775 NSApplicationMain + 777
     12 libdyld.dylib 0x00007fff69e457fd start + 1

     Thread 1 :
     0 libsystem_pthread.dylib 0x00007fff6a045818 start_wqthread + 0

     Thread 2 :
     0 libsystem_pthread.dylib 0x00007fff6a045818 start_wqthread + 0

     Thread 3 Crashed: : Dispatch queue : com.dummyapps.videoBrowser.screenshot
     0 ??? 0x00000001134b5000 0 + 4618670080
     1 com.dummyapp.VideoBrowserLite 0x000000010f728510 0x10f6d9000 + 324880