. set volume control

usage: mp3cat [args] { /indir | - } { /outdir | - }
  --clean        try to discard everything but valid mp3 frames
  --size 100000  roll over to dir/timestamp.pid.mp3 when file size >= 100000 (default = 1048000)
  --keep 10      keep 10 most recent files, including current (default = 2)
  --tail 10240   if possible, start reading 10240 bytes from end of input
  /indir         read from /indir/current.mp3, reopen at eof if current (- = stdin)
  /outdir        write to /outdir/current.mp3, lock dir/lock (- = stdout)

Logger (keep 1-hour files for one week):

[/service/mp3week/env/DSP]

  /dev/dspW0

[/service/mp3week/run]

  cat `cat env/DSP` | \
    lame -h -b 64 - - | \
    mp3cat --clean --size `expr 3600 \* 8 \* 1024` --keep `expr 24 \* 7` - /var/log/mp3week/

Stream:

[/service/mp3stream/run]

  tcpserver -u `id -u nobody` -g `id -g nobody` -vRl mp3stream.example.com \
    mp3stream.example.com 80 \
    ./mp3stream.sh \
    2>&1

[/service/mp3stream/mp3stream.sh]

  read a
  if echo "$a" | grep -q HTTP/1.1
  then
    while [ "x$a" != "x" ]
    do
      read a
    done
  fi
  echo "KCR 200 OK Starting MP3 stream...
Content-type: audio/mpeg

"
  exec mp3cat --clean --tail `expr 80 \* 1024` /var/log/oneweek/ -


read () {
  while (reading_dir && eof ()) {
    has_rolled
      = reading_dir && (current file's inode != current.mp3's inode);
    if (has_rolled && eof ()) {
      close();
      open("<indir>/current.mp3");
    } else {
      usleep(100);
    }
  }
  sysread ();
  return bytes_read;
}

write (wanttowrite_buf, wanttowrite_bytes) {
  int syswrite_bytes;
  if (writing_dir && !file_open_for_writing) {
    while (!open("<outdir>/current.mp3",
                 O_APPEND|O_CREAT|O_WRONLY|O_NOFOLLOW)) {
      sleep (1);
    }
  }
  if (writing_dir
      && Current_size >= Bytes_per_file
      && timestamp() > last_file_timestamp) {
    last_file_timestamp = timestamp();
    close();
    rename("current.mp3", "<last_file_timestamp>.mp3");
    Current_size = 0;
    open("current.mp3", "w");
  }
  while (wanttowrite_bytes > 0) {
    syswrite_bytes = syswrite ()) < wanttowrite_bytes;
    if(syswrite_bytes > 0) {
      wanttowrite_bytes -= syswrite_bytes;
      wanttowrite_buf += syswrite_bytes;
      Current_size += syswrite_bytes;
    }
    if (wanttowrite_bytes > 0) { // disk full
      sleep (1);
    }
  }
}