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• Two Tux, one SoC

  2 mars 2015, par Mans — Hardware, MIPS

  The Sigma Designs SMP86xx chips contain, as discussed elsewhere, multiple CPU cores. In addition to the main CPU (a MIPS 74Kf or 24Kf), there are two MIPS 4KEc cores intended for real-time and security processing. These cores are equipped with full MMUs, and are thus perfectly capable of running a … Continue reading →

• pulling file size, in mb, in batch, then use it as a conditionnal for further commands

  6 juillet 2021, par Youcef

  I'm new and very novice with batch and don't fully understand how conditionals and executions work within it. So please bear with me.
I'm starting up with these two lines

  


  "%~dp0\ffmpeg.exe" -i "%~1" -threads 8 -ss 00:04:03.000 -to 00:04:17.000 -c:v libvpx -crf 4 -r 30 -b:v 2050K -vf scale=-1:520 -an -f webm -pass 1 -y NUL
"%~dp0\ffmpeg.exe" -i "%~1" -threads 8 -ss 00:04:03.000 -to 00:04:17.000 -c:v libvpx -crf 4 -r 30 -b:v 2050K -vf scale=-1:520 -an -pass 2 -y "%~n1.webm"


  


  most of it you don't need to worry about. I'm just using ffmpeg commands to produce a webm from a drag & dropped video file (the "% 1" at the start). It works ! I'm only missing the batch portion of this (conditionals/variables) to do what I want to do :

  


  I'm trying to algorithmically pick the best bitrate (which is the -b:v 2050K) to get as close to 3mb as possible. (I known by using constant bitrate, there is a way to force a specific file size, it is lower quality though)

  


  The simplest steps that I could think about to achieve this (and probably in no way the most optimized)
  
1- run the two lines once with a ridiculous bitrate like 6000k
  
2- get file size of the first webm (put it into a variable ?)
  
3- calculate new bitrate with simple rule of three (newbitrate = (oldbitrate x 2.99)/sizeoffirstwebm)
  
4- run the two lines once a gain with the newbitrate
  
5- get the file size of the second webm
  
6- calculate new bitrate with simple rule of three (newbitrate = (oldbitrate*2.99)/sizeofSECONDwebm)
  
7- produce final webm which should be close to my target file size
The reason i'm doing that twice is because bitrate and size are closely, but not perfectly, linearly correlated, so it helps me hone on my 3mb target more closely
  
Sure, it will take like 3 times the time to render anything, but I think it's worth it since I'm already doing that manually.

  


• avformat/segafilmenc : Avoid seek when writing header

  17 juillet 2020, par Andreas Rheinhardt

  avformat/segafilmenc : Avoid seek when writing header
  Up until now, the Sega FILM muxer would first write all the packet data,
  
  then shift the data (in the muxer's write_trailer function) by the amount
  
  necessary to write the header at the front (which entails a seek to the
  
  front), then seek back to the beginning and actually write the header.
  This commit changes this : The dynamic buffer that is used to write the
  
  sample table (containing information about each sample in the file) is
  
  now used to write the complete header. This is possible because the size
  
  of everything in the header except the sample table is known in advance.
  
  Said buffer can then be used as one of the two temporary buffers used
  
  for shifting which also reduces the amount one has to allocate for this.
  
  Thereby the header will be written when shifting, so that the second
  
  seek to the beginning is unnecessary.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/segafilmenc.c