cap.sh

#!/bin/bash

################################################################################
# cap - capture your screen
#
# This script allows you to capture your screen on Linux or macOS systems using
# the appropriate tools available on each platform. On Linux, it uses 'slop'
# and 'ffmpeg', while on macOS, it utilizes 'screencapture'. The script prompts
# you to select a desktop area for recording and saves the recording as an MP4/MOV
# file with customizable video quality.
#
# Usage: cap [options] <output.mp4>
#
# Options:
#   -v, --version        Display script version
#   -h, --help           Display this help message
#   -q, --quality <num>  (only for Linux) Specify the video quality in the range
#                        0-51 (best/worst) (default: 28)
#
# Requirements:
#   - For Linux: slop, ffmpeg
#   - For macOS: screencapture
################################################################################


# Function to display script version
show_version() {
  echo "cap - capture your screen - 0.0.1"
}

# Function to display script usage
show_usage() {
  echo "Usage: $0 [options] <output.mp4>"
  echo "Options:"
  echo "  -v, --version        Display script version"
  echo "  -h, --help           Display this help message"
  echo "  -q, --quality <num>  (only for Linux) Specify the video quality in range 0–51(best/worst)(default: 28)"
}

# Function to check if the required command exists
check_command() {
  if ! command -v $1 &> /dev/null
  then
    echo "$1 command not found. Please install $1."
    exit 1
  fi
}

# Function to check if an output filename was provided
check_filename() {
  if [ -z "$1" ]; then
    echo "Usage: $0 [options] <output.mp4>"
    exit 1
  fi
}

run_checks() {

  # Check the operating system
  if [[ "$OSTYPE" == "linux-gnu"* ]]; then
    # Check if an output filename was provided
    check_filename "$1"
    # Set the output file name
    filename="$1"
    system="linux"

    echo "Identified a Linux system... using 'slop' and 'ffmpeg'"

    check_command "ffmpeg"
    check_command "slop"

  elif [[ "$OSTYPE" == "darwin"* ]]; then
    system="macos"
    commandtool="screencapture"
    echo "Identified a macOS system... using 'screencapture'"
    check_command "screencapture"

  else
    echo "Unsupported operating system."
    exit 1

  fi
  # Process command line options
  handle_options "$@"

}

# Function to start the recording
start_recording() {

  if [[ $system == "linux" ]]; then
    # Set log level to quiet (suppress console output)
    # Input format: X11 screen capture
    # Set input video size (width x height)
    # Input device: X11 display with specified position (x, y)
    # Input audio device: ALSA pulse audio
    # Video codec: libx264 (H.264)
    # Constant Rate Factor: video quality setting (lower value = higher quality)
    # Set encoding preset to ultrafast for fast encoding
    # Optimize for low latency streaming
    # Set pixel format to yuv420p (YUV planar 4:2:0)
    # Output format: MP4
    # Output file name
    echo "Recording started. Press 'q' to stop recording."
    ffmpeg -loglevel quiet \
    -f x11grab \
    -s ${width}x${height} \
    -i ${DISPLAY}+$x,$y \
    -f alsa -i pulse \
    -c:v libx264 \
    -crf $quality \
    -preset ultrafast \
    -tune zerolatency \
    -pix_fmt yuv420p \
    -f mp4 \
    $filename

  else
    screencapture -vksU -

  fi
}

# Function to handle command line options
handle_options() {
  while [[ $# -gt 0 ]]; do
    case "$1" in
      -v|--version)
        show_version
        exit 0
        ;;
      -h|--help)
        show_usage
        exit 0
        ;;
      -q|--quality)
        shift
        quality="$1"
        echo "Quality set to $quality"
        ;;
      *)
        break
        ;;
    esac
    shift
  done
}

# Default quality value
quality=28

run_checks "$@"

if [[ "$system" == "linux" ]]; then
  # Get the selection coordinates
  coords=$(slop -f "%x %y %w %h")

  # Extract the x, y, width, and height values from the coordinates
  x=$(echo $coords | awk '{print $1}')
  y=$(echo $coords | awk '{print $2}')
  width=$(echo $coords | awk '{print $3}')
  height=$(echo $coords | awk '{print $4}')

  # Ensure that the height and width are divisible by 2
  width=$((width / 2 * 2))
  height=$((height / 2 * 2))

  # Start the recording
  start_recording

  # Display message to user
  echo "Recording stopped."

elif [[ "$system" == "macos" ]]; then
  start_recording
  echo "Recording can be found in your desktop."

fi

I like this Idea a lot, however the framerate of the resulting video is really bad. The file claims to be 60fps. but the resulting video is extremely choppy, more like 5 fps:

2024-10-13_11-11-01.webm.mov

I tried playing around with the -framerate 30 option of ffmpeg, but the result is still choppy.
Any idea how to fix that?

It seems like using libx264rgb instead of libx264 as suggested here increases fps a lot, but the result still is kinda choppy:

2024-10-13_11-27-44.webm.mov

Maybe using hardware encoding is the way to go.

On my AMD GPU machine using h264_amf insgtead of libx264 results in smooth video (as long as the resolution is not too big):

2024-10-13_11-30-59.webm

Hi @markusressel

I'm glad you found this little script interesting/useful.

I am not an expert when it comes to video configuration tbh, but, as you have tried, it would be a matter of trying maybe different libs and/or video codecs.

FFMPEG is a versatile tool but it does come with a steep learning curve but I am sure you can tweak the script to find the expected quality.

Sorry I couldn't be of more help!