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• lavu/riscv : helper macro for VTYPE encoding

  5 octobre 2022, par Rémi Denis-Courmont

  lavu/riscv : helper macro for VTYPE encoding
  On most cases, the vector type (VTYPE) for the RISC-V Vector extension
  
  is supplied as an immediate value, with either of the VSETVLI or
  
  VSETIVLI instructions. There is however a third instruction VSETVL
  
  which takes the vector type from a general purpose register. That is so
  
  the type can be selected at run-time.
  This introduces a macro to load a (valid) vector type into a register.
  
  The syntax follows that of VSETVLI and VSETIVLI, with element size,
  
  group multiplier, then tail and mask policies.
  

  • [DH] libavutil/riscv/asm.S

• How to pipe live video frames from ffmpeg to PIL ?

  30 janvier 2017, par Ryan Martin

  I need to use ffmpeg/avconv to pipe jpg frames to a python PIL (Pillow) Image object, using gst as an intermediary*. I’ve been searching everywhere for this answer without much luck. I think I’m close - but I’m stuck. Using Python 2.7

  My ideal pipeline, launched from python, looks like this :

  1. ffmpeg/avconv (as h264 video)
  2. Piped ->
  3. gst-streamer (frames split into jpg)
  4. Piped ->
  5. Pil Image Object

  I have the first few steps under control as a single command that writes .jpgs to disk as furiously fast as the hardware will allow.

  That command looks something like this :

  command = [
  
          "ffmpeg",
  
          "-f video4linux2",
  
          "-r 30",
  
          "-video_size 1280x720",
  
          "-pixel_format 'uyvy422'",
  
          "-i /dev/video0",
  
          "-vf fps=30",
  
          "-f H264",
  
          "-vcodec libx264",
  
          "-preset ultrafast",
  
          "pipe:1 -",
  
          "|", # Pipe to GST
  
          "gst-launch-1.0 fdsrc !",
  
          "video/x-h264,framerate=30/1,stream-format=byte-stream !",
  
          "decodebin ! videorate ! video/x-raw,framerate=30/1 !",
  
          "videoconvert !",
  
          "jpegenc quality=55 !",
  
          "multifilesink location=" + Utils.live_sync_path + "live_%04d.jpg"
  
        ]

  This will successfully write frames to disk if ran with popen or os.system.

  But instead of writing frames to disk, I want to capture the output in my subprocess pipe and read the frames, as they are written, in a file-like buffer that can then be read by PIL.

  Something like this :

      import subprocess as sp
  
      import shlex
  
      import StringIO
  
  
  
      clean_cmd = shlex.split(" ".join(command))
  
      pipe = sp.Popen(clean_cmd, stdout = sp.PIPE, bufsize=10**8)
  
  
  
      while pipe:
  
  
  
          raw = pipe.stdout.read()
  
          buff = StringIO.StringIO()
  
          buff.write(raw)
  
          buff.seek(0)
  
  
  
          # Open or do something clever...
  
          im = Image.open(buff)
  
          im.show()
  
  
  
          pipe.flush()

  This code doesn’t work - I’m not even sure I can use "while pipe" in this way. I’m fairly new to using buffers and piping in this way.

  I’m not sure how I would know that an image has been written to the pipe or when to read the ’next’ image.

  Any help would be greatly appreciated in understanding how to read the images from a pipe rather than to disk.

  • This is ultimately a Raspberry Pi 3 pipeline and in order to increase my frame rates I can’t (A) read/write to/from disk or (B) use a frame by frame capture method - as opposed to running H246 video directly from the camera chip.

• FFMPEG - Add (white, color-less, analog) grain to the video without desaturating video itself

  2 décembre 2018, par dd_code

  I am working on old videos where I am basically converting them to HVEC and sharpening, so i.e. my command can look like this

  .\ffmpeg.exe -i F:\file.mkv -vf unsharp=3:3:1.5 -c:v hevc_nvenc -qp 27 -a:c copy file_new.mkv

  inherent problem with this is, of course that with reducing bitrate and sharpening every now and then I can notice some nasty artifacts around the edges and on at plain-color objects.

  I noticed with some older, many times remastered movies/series that they have quite a lot of grain in the video, so I was thinking - what if I add grain and help it to mask the compression and sharpening artifacts ?

  After bit of searching I got to
  https://ffmpeg.org/ffmpeg-filters.html#noise
  and now I am using this command

  .\ffmpeg.exe -i F:\file.mkv -vf unsharp=3:3:1.5,noise=alls=14:allf=t+u -c:v hevc_nvenc -qp 30 -a:c copy file_new.mkv

  however this has one big problem, it is merely a digital RGB noise, is there a way to make it desaturated, analog-ish ? I tried adding h=s=0, however this is applying 0 saturation to the video track as a whole. Is there an effect which would achieve this or is there a way that I can reduce the saturation only of the very effect which then gets to "overlay" the video track, so the track would not be touched ?