Recherche avancée

Sur d’autres sites (6066)

• Naive Sorenson Video 1 Encoder

  12 septembre 2010, par Multimedia Mike — General

  (Yes, the word is “naive” — or rather, “naïve” — not “native”. People always try to correct me when I use the word. Indeed, it should actually be written with 2 dots over the ‘i’ but who has a keyboard that can easily do that ?)

  At the most primitive level, programming a video encoder is about writing out a sequence of bits that the corresponding video decoder will understand. It’s sort of like creating a program — represented as a stream of opcodes — that will run on a given microprocessor or virtual machine. In fact, reading a video codec bitstream specification will reveal a lot of terminology along the lines of “transmitting information to the decoder” or “signaling the decoder to do xyz.”

  Creating a good encoder that will deliver decent quality at a reasonable bitrate is difficult. Creating a naive encoder that produces a technically compliant bitstream, not so much.

  
  
  

  When I wrote an FFmpeg encoder for Sorenson Video 1 (SVQ1), the first step was to just create a minimally compliant bitstream. The coarsest encoding mode that SVQ1 allows is to encode the average (mean) of each 16×16 block of samples. So I created an encoder that just encoded the mean of each block. Apple’s QuickTime Player was able to play the resulting video in all of its blocky glory. The result rather reminds me of the Super Nintendo’s mosaic effect.

  Level 5 blocks (mean-only 16×16 encoding) :
  

  
  
  

  Level 3 blocks (mean-only 8×8 encoding) :
  

  
  
  

  It’s one thing for your own decoder (in this case, FFmpeg’s own decoder) to be able to decode the data. The big test is whether the official decoder (in this case, Apple QuickTime Player) can decode the file.

  
  
  

  Now that’s a good feeling. After establishing that sort of baseline, it’s possible to adapt more and more features of the codec.

• How can start a process and stop the process if "error" string appear in the console output strings in one line commands set

  25 janvier 2018, par Thm Lee

  Now I want one line cmd commands set which start a process and monitor the consol output strings stream. And so if error message appear in the process’s console output, then could stop the process immediately.

  For example, I tried below commends sets, but failed. It seems find command didn’t get any strings streams in which search key word "error"

  ffmpeg "endcoding process options set" | find "error" && exit

  or,

  ffmpeg "endcoding process options set" 2>&1 find "error" && exit

  Is there any solutions about this ?

  Thanks in advance

• checkasm : arm : preserve the stack alignment in x264_checkasm_checked_call

  14 novembre 2016, par Janne Grunau

  checkasm : arm : preserve the stack alignment in x264_checkasm_checked_call
  The stack used by x264_checkasm_checked_call_neon was a multiple of 4
  
  when the checked function is called. AAPCS requires a double word (8 byte)
  
  aligned stack public interfaces. Since both calls are public interfaces
  
  the stack is misaligned when the checked is called.
  This can cause issues if code called within this (which includes
  
  the C implementations) relies on the stack alignment.
  

  • [DH] tools/checkasm-arm.S