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• avcodec/dovi_rpu{enc,dec} : fix ms_weight handling

  25 mai 2024, par Niklas Haas

  avcodec/dovi_rpuenc,dec : fix ms_weight handling
  The code as written was wrong. In the spec, these fields are treated
  
  merely as plain integers in the range 0 to 4095. The only difference
  
  between L2 and L8 is that L2.ms_weight also accepts an additional value
  
  of -1, hence the extra sign bit. While it's likely that these are still
  
  shifted integers in disguise, since all real-world samples seem to use
  
  a value of 2048 here, the offset used in the code was wrong.
  In addition, because the l8.ms_weight struct member is unsigned, these
  
  wrong shifting semantics ended up overflowing the field, leading to
  
  undefined behavior when transcoding. Fortunately, the damage was
  
  relatively contained in practice, because it just corrupts the coding of
  
  this field, which is ignored in practice in all implementations I have
  
  seen.
  

  • [DH] libavcodec/dovi_rpudec.c
  • [DH] libavcodec/dovi_rpuenc.c

• How to restrict fetching hls segment files on pause in Safari (MacOS and iOS)

  24 juillet 2021, par Charan Kumar

  We generate hls files with segment size of 3 seconds. We use hlsjs for non Safari browsers and Safari has native hls support.

  


  In hlsjs world we were able to restrict how much ahead we should be in terms of buffer using maxMaxBufferLength, where as we are unable to find similar solution for Safari. In Safari, after loading video m3u8, even if I pause after a second, in the network tab I can see that all the segments are being fetched which I would like to restrict.

  


  I'll not be able to share our examples due to company polices. But, a public example file by hls.js is attached below :

  


  https://test-streams.mux.dev/x36xhzz/url_6/193039199_mp4_h264_aac_hq_7.m3u8 try opening this url in Safari, and try pausing the video, you'll see that it continues to download. Where as if you open same one using https://hls-js.netlify.app/demo/ with maxMaxBufferLength : 5 it won't happen.

  


  Is there an option at ffmpeg to make it controlled buffer or some solution that we should do for Safari by listening to events ?

  


  Found the same question here -> https://developer.apple.com/forums/thread/121074

  


• Building FFMPEG for Visual Studio development

  28 juillet 2016, par gboy

  I’m trying to use ffmpeg in Visual Studio 2013 C++ software (ultimately as part of an OpenCV project) - but right now I’m just trying to get basic FFMPEG functionality. In general, when building in Visual Studio, I build 64—bit software with Multi-threaded DLL runtime libraries. I have built ffmpeg using the general instructions for ’Native Windows compilation using ... MinGW-w64’ at http://ffmpeg.org/platform.html#Windows (I provide a more detailed set of steps I followed below...).

  After building the ffmpeg software on my system, I tried to create a simple ’hello world’ project in Visual Studio 2013. Specifically, I tried to implement the initial tutorial file presented at http://dranger.com/ffmpeg/tutorial01.html. Upon building the project, I get the error :

  c :\msys64\usr\local\ffmpeg\libavutil\common.h(45) : fatal error C1083 : Cannot
  open include file : ’libavutil/avconfig.h’ : No such file or directory

  The following are the detailed steps I took to build ffmpeg and create my basic Visual Studio project :

  ============ Building ffmpeg ===============

  1. Downloaded and intalled msys2-x86_64-20160205.exe from http://msys2.github.io
  2. Ran update-core to update the Msys2 install
  3. Ran pacman -Suu (twice) to complete the update (following the instructions about updating shortcuts, etc.)
  4. Then I quit out of the MSys2 shell and opened the MinGW-w64 Win64 Shell. In this new shell :
  5. Installed the following packages using pacman -S The list of packages I installed is : make, pkg-config, diffutils, mingw-w64-x86_64-yasm, mingw-w64-x86_64-gcc, mingw-w64-x86_64-SDL, git
  6. Then I cd’d into cd /usr/local
  7. Ran git clone https://git.ffmpeg.org/ffmpeg.git ffmpeg
  8. I wanted to build the ffmpeg library ’out-of-tree’ of this MSys64 folder. So, in the regular file system of my Windows machine I created a folder at C :\ffmpeg
  9. Back in the Win64 Shell, I cd’d to this new folder : cd /c/ffmpeg
  10. Then ran /usr/loca/ffmpeg/configure --enable-shared
  11. Then make -r
  12. And, finally make install

  Now, if I had to guess, my ’flaw’ was in the options I used when calling the ’configure’ script of ffmpeg. Do I need to use particular options so that I can take the ffmpeg libraries built here and use them as dynamic (DLL) libraries in Visual Studio ?

  ========== Configuring my Visual Studio Project ============

  Here’s how I created a simple hello world project in Visual Studio to see if ffmpeg is working.

  1. I created a new Visual C++ ’Empty Project’ in Visual Studio 2013

  2. I then configured the project properties as follows :

     a. In C/C++ => General => Additional Include Directories, I put

     C :\msys64\usr\local\ffmpeg

     b. In Linker=>General => Additional Library Directories, I pointed to each of the built library folders (basically I pointed at all of the libraries that were built to ensure I was not inadvertently missing the critical one). The list is as follows :

     • C :\ffmpeg\libavcodec
     • C :\ffmpeg\libavdevice
     • C :\ffmpeg\libavfilter
     • C :\ffmpeg\libavformat
     • C :\ffmpeg\libavutil
     • C :\ffmpeg\libswresample
     • C :\ffmpeg\libswscale
     • C :\ffmpeg

     c. In Linker=> Input => Additional Dependencies, I pointed to the particular libraries (again - I pointed to all of the ones present). The list is :

     • avcodec.lib
     • avdevice.lib
     • avfilter.lib
     • avformat.lib
     • avutil.lib
     • swresample.lib
     • swscale.lib

  3. I then created a new source file called ’tut01.c’ and copied/pasted the code from http://dranger.com/ffmpeg/tutorial01.c

  4. Then hit F7 and got the error specified above about not finding avconfig.h

  The above is my best guess as to the steps I need to follow to get this working in Windows (btw, it’s Windows 10, 64-bit) & Microsoft Visual Studio 2013. What should I change to get this basic program to build and run ?