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• aarch64 : NEON asm for integral init

  14 août 2014, par Janne Grunau

  aarch64 : NEON asm for integral init
  integral_init4h_neon and integral_init8h_neon are 3-4 times faster than
  
  C. integral_init8v_neon is 6 times faster and integral_init4v_neon is 10
  
  times faster.
  

  • [DH] common/aarch64/mc-a.S
  • [DH] common/aarch64/mc-c.c

• ffmpeg pipe blocks while capturing

  26 juin 2013, par Marco Vasapollo

  I have this code :

  public InputStream getInputStream() throws Exception {
  
      try {
  
          process = Runtime.getRuntime().exec("ffmpeg -f dshow -i video=\"" + query + "\":audio=\"" + microPhoneName + "\" -r 25 -vcodec mpeg4 -acodec mp3 -f avi -");
  
          } 
  
          catch (Exception e) {
  
          }
  
      return process.getInputStream();
  
  }

  When i use the inputStream.read(b) command, it works only for a little bit of times (180 to 400 times, depending from formats and codecs I use) then the inputStream lock on read and the application doesn't go anymore.

  What's the problem ? Memory saturation (ffmpeg process memory is at least 14mb) ?
  Is there a way to unlock this situation (clean memory, use a file as a bridge to prevent locks) ?

  Of course I need a little bit of "realtime", and not "post-process".
  I'm not constrained to use ffmpeg, I can change it if necessary.

• Trimming videos with 'ffmpeg and ffprobe'

  10 août 2022, par adeshina Ibrahim

  I am working on an ETL process, and I'm now in the final stage of preprocessing my videos. I used the script below (reference : @FarisHijazi) to first auto detected black-screen frames using ffprobe and trim them out using ffmpeg.

  


  The script worked for me but the problems are :

  


  


  1. It cut off all other good frames together with the first bad frames. e.g. if gBgBgBgB represents a sequence of good and BAD frames for 5sec each, the script only returned the first g(5sec) and cut off the other BgBgBgB after it. I want to have only g g g g where all B B B B has been removed

     


  


  2. I also want to detect other colors aside black-screen e.g. green-screen or red-screen or blurry part of video

     


  


  3. Script doesn't work if video has no audio in it.

     


  


  


  import argparse
import os
import shlex
import subprocess

parser = argparse.ArgumentParser(
    __doc__, formatter_class=argparse.ArgumentDefaultsHelpFormatter
)
parser.add_argument("input", type=str, help="input video file")
parser.add_argument(
    "--invert",
    action="store_true",
    help="remove nonblack instead of removing black",
)
args = parser.parse_args()

##FIXME: sadly you must chdir so that the ffprobe command will work
os.chdir(os.path.split(args.input)[0])
args.input = os.path.split(args.input)[1]

spl = args.input.split(".")
outpath = (
    ".".join(spl[:-1])
    + "."
    + ("invert" if args.invert else "")
    + "out."
    + spl[-1]
)


def delete_back2back(l):
    from itertools import groupby

    return [x[0] for x in groupby(l)]


def construct_ffmpeg_trim_cmd(timepairs, inpath, outpath):
    cmd = f'ffmpeg -i "{inpath}" -y -r 20 -filter_complex '
    cmd += '"'
    for i, (start, end) in enumerate(timepairs):
        cmd += (
            f"[0:v]trim=start={start}:end={end},setpts=PTS-STARTPTS,format=yuv420p[{i}v]; "
            + f"[0:a]atrim=start={start}:end={end},asetpts=PTS-STARTPTS[{i}a]; "
        )
    for i, (start, end) in enumerate(timepairs):
        cmd += f"[{i}v][{i}a]"
    cmd += f"concat=n={len(timepairs)}:v=1:a=1[outv][outa]"
    cmd += '"'
    cmd += f' -map [outv] -map [outa] "{outpath}"'
    return cmd


def get_blackdetect(inpath, invert=False):
    ffprobe_cmd = f'ffprobe -f lavfi -i "movie={inpath},blackdetect[out0]" -show_entries tags=lavfi.black_start,lavfi.black_end -of default=nw=1 -v quiet'
    print("ffprobe_cmd:", ffprobe_cmd)
    lines = (
        subprocess.check_output(shlex.split(ffprobe_cmd))
        .decode("utf-8")
        .split("\n")
    )
    times = [
        float(x.split("=")[1].strip()) for x in delete_back2back(lines) if x
    ]
    assert len(times), "no black scene detected"

    if not invert:
        times = [0] + times[:-1]
    timepairs = [
        (times[i], times[i + 1]) for i in range(0, len(times) // 2, 2)
    ]
    return timepairs


if __name__ == "__main__":
    timepairs = get_blackdetect(args.input, invert=args.invert)
    cmd = construct_ffmpeg_trim_cmd(timepairs, args.input, outpath)

    print(cmd)
    os.system(cmd)