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• images->video->web canvas : RGB/YUV issues

  5 février 2016, par nrob

  We’ve written an web app which :

  1. takes 3D, time dependent weather data
  2. tiles each 3D time point to make a 2D frame (written out as a png image)
  3. stitches these frames together into a video (using ffmpeg/avconv)
  4. streams this video into a web app
  5. polls the canvas for frames
  6. sends the frames to the GPU where they are converted back to 3D and ray traced

  You can see the app here, code here and you can see the data video here

  Currently the pngs are written as RGB images, the video codec is in YUV and getting frames from the canvas returns RGB. As such there is a significant loss of information due to the conversion between image spaces.

  Does anyone have suggestions what is the best way round this ?

  I’ve tried a bunch of RGB video codecs, but I can’t get any to work, and I don’t know if the web browser will support it anyway. Can anyone suggest a good RGB codec (both lossy and lossless would be great)

  Also, is it possible to write to YUV images/read them from a video canvas in HTML5 ?

  Ultimately, I don’t even want anything to do with images/videos, I’m just hacking the codecs to stream/compress large animated 3D data volumes

• Location of the amd64 compiler in Visual Studio 2022 | Compiling FFmpeg with NVENC

  6 juin 2022, par Gal Grünfeld

  I'm trying to follow Nvidia's guide to compile FFmpeg with nvenc support on Windows and it has a stage to export the path of Visual Studio's 2013 SP2 amd64 compiler to the global path variable of the compilation dev environment :

  


  


  export PATH="/c/Program Files (x86)/Microsoft Visual Studio 12.0/VC/BIN/amd64/" :$PATH

  


  


  They say earlier in the guide that for different versions of Visual Studio different path might be required. I'm trying to use Visual Studio 2022 Community, but don't know where its amd64 compiler directory is.
I also don't know what that VC stands for ("Visual C", maybe, whatever that "Visual" might mean ?).

  


  I found in the installation directory of Visual Studio 2022 a few directories named amd64 but none of them were under one with VC or something similar in its name.
The one I think is the most likely candidate to be the updated compiler is at /MSBuild\Current\Bin\amd64.

  


  If anyone knows, please tell me if if this is the right path, and if not, what is the right path.

  


  Microsoft does offer a version of Visual Studio 2013 Update 2, though (I assume they changed their naming scheme from "service packs" to "updates, which would make it the same software), but it doesn't offer a 64-bit version of it, and I want to compile a 64-bit software - so I assume it doesn't come with one. Please do correct me if I'm wrong, it'd save me needing to use a version of Visual Studio that is different than the one in the guide.

  


• ffmpeg : segment muxer cutting segments early

  4 mars 2020, par M. Parker

  My current project is an attempt to use the segment muxer to divide an input stream into mp4 files of a particular duration (say, 3 seconds). Use of the segment_time option after allocating the muxer ought to have me covered. What I am seeing is segmenting based on a particular number of data units. If I try to copy the stream, it will cut the segment after 16 AVPackets have been sent to the output stream. If I try to encode it (libx264), the file will instead be written after 16 AVFrames. Changing the segment_time variable doesn’t alter the number of units written/file length, although larger numbers can result in errors. I figure I have to be missing something obvious. Any ideas ?