A guide to video and audio editing in R, covering tasks like checking and changing resolution, length, and size, as well as cropping and converting formats.

video/audio editing include change resolution and length

This document provides a comprehensive guide to video and audio editing using R, with a focus on the av package. It covers a wide range of tasks, from basic checks like determining video resolution and length to more advanced operations like changing video resolution, trimming video length, cropping, and converting video to images or audio-only formats. The audio section demonstrates how to manipulate MP3 files, including changing their length and converting them to WAV format.

Original video:

Video

Code

library(tidyverse)
library(av)

check video resolution

Code

get_video_resolution_ffmpeg <- function(file_path) {
  if (!file.exists(file_path)) {
    stop("File does not exist.")
  }
  # Run ffmpeg command and capture output
  cmd <- sprintf("ffmpeg -i %s 2>&1", shQuote(normalizePath(file_path)))
  output <- system(cmd, intern = TRUE, ignore.stderr = FALSE)
  # Find the line containing video stream details
  video_line <- grep("Video:", output, value = TRUE)
  if (length(video_line) == 0) {
    stop("No video stream found.")
  }
  # Extract resolution using regex (e.g., 1920x1080)
  resolution <- regmatches(video_line, regexpr("\\d{3,}x\\d{3,}", video_line))
  if (length(resolution) == 0) {
    stop("Resolution not detected.")
  }
  dimensions <- as.numeric(strsplit(resolution, "x")[[1]])
  return(dimensions)
}

Code

resolution <- get_video_resolution_ffmpeg("demo.mp4")
cat(sprintf("Resolution: %dx%d", resolution[1], resolution[2]))

Resolution: 960x720

check video length and size

Code

video_info <- av::av_media_info("demo.mp4")
video_length <- video_info$duration
cat("video length:",video_length)

video length: 30.02501

Code

video_size_mb <- file.info("demo.mp4")$size / (1024^2)
cat("video size in mb:",video_size_mb)

video size in mb: 1.029325

change video resolution

Code

# Input video file path
input_video <- "demo.mp4"

# Output video file path
output_video <- "demo_resolution.mp4"

# Desired width and height
new_width <- 960/3*2
new_height <- 720/3*2

# Construct the FFmpeg command for resizing
ffmpeg_command <- paste0(
  "ffmpeg -i '", input_video, "' -vf scale=", new_width, ":", new_height, " '", output_video, "'"
)

# Execute the FFmpeg command
system(ffmpeg_command)

cat("Video resized to", new_width, "x", new_height, "and saved to", output_video, "\n")

Video resized to 640 x 480 and saved to demo_resolution.mp4

Video after change resolution:

Code

resolution <- get_video_resolution_ffmpeg(output_video)
cat(sprintf("Resolution: %dx%d", resolution[1], resolution[2]))

Resolution: 640x480

Code

video_info <- av::av_media_info(output_video)
video_length <- video_info$duration
cat("video length:",video_length)

video length: 30.02501

Code

video_size_mb <- file.info(output_video)$size / (1024^2)
cat("video size in mb:",video_size_mb)

video size in mb: 0.72155

change length of video

Code

# Define input/output files and timestamps
input_file <- "demo.mp4"

# Define input and output file paths
input_video <- "demo.mp4"
output_video <- "demo_change_length.mp4"

# --- Example 1: Trimming from the beginning ---
start_time <- "00:00:05" # Start at 5 seconds
duration <- "00:00:10"  # Keep for 10 seconds

command_trim <- sprintf("ffmpeg -i %s -ss %s -t %s  %s",
                        input_video, start_time, duration, output_video)

#command_trim
system(command_trim)
cat(paste("Trimmed video saved to:", output_video, "\n"))

Trimmed video saved to: demo_change_length.mp4

Video after change length:

Code

video_info <- av::av_media_info("demo_change_length.mp4")
video_length <- video_info$duration
cat("video length:",video_length)

video length: 10

Code

video_size_mb <- file.info("demo_change_length.mp4")$size / (1024^2)
cat("video size in mb:",video_size_mb)

video size in mb: 0.275506

video Crop

Code

# Define the path to the input video file
input_video_path <- "demo.mp4"  # Replace with your video file path

# Define the path to save the cropped video
output_video_path <- "demo_crop.mp4"  # Replace with your desired output path

# Define crop parameters
crop_width <- 640   # Desired width of the cropped video
crop_height <- 360  # Desired height of the cropped video
crop_x <- 100       # X offset for cropping
crop_y <- 50        # Y offset for cropping

# Define the crop filter
crop_filter <- sprintf("crop=%d:%d:%d:%d", crop_width, crop_height, crop_x, crop_y)

# Crop the video
av::av_encode_video(
  input = input_video_path,
  output = output_video_path,
  vfilter = crop_filter,
  audio=input_video_path
)

[1] "/Users/jinchaoduan/Documents/Project/Tech-blog/posts/edit video/demo_crop.mp4"

Code

cat("Video cropped successfully and saved to:", output_video_path, "\n")

Video cropped successfully and saved to: demo_crop.mp4

Video after crop:

video to image

Code

# Convert MP4 to images (frames)
av_video_images(
  video = "demo.mp4", 
  destdir = "output_img",  # Save frames as PNG files
  format = "jpg",
  fps = 1  # Extract 1 frame per second (adjust FPS as needed)
)

 [1] "output_img/image_000001.jpg" "output_img/image_000002.jpg"
 [3] "output_img/image_000003.jpg" "output_img/image_000004.jpg"
 [5] "output_img/image_000005.jpg" "output_img/image_000006.jpg"
 [7] "output_img/image_000007.jpg" "output_img/image_000008.jpg"
 [9] "output_img/image_000009.jpg" "output_img/image_000010.jpg"
[11] "output_img/image_000011.jpg" "output_img/image_000012.jpg"
[13] "output_img/image_000013.jpg" "output_img/image_000014.jpg"
[15] "output_img/image_000015.jpg" "output_img/image_000016.jpg"
[17] "output_img/image_000017.jpg" "output_img/image_000018.jpg"
[19] "output_img/image_000019.jpg" "output_img/image_000020.jpg"
[21] "output_img/image_000021.jpg" "output_img/image_000022.jpg"
[23] "output_img/image_000023.jpg" "output_img/image_000024.jpg"
[25] "output_img/image_000025.jpg" "output_img/image_000026.jpg"
[27] "output_img/image_000027.jpg" "output_img/image_000028.jpg"
[29] "output_img/image_000029.jpg" "output_img/image_000030.jpg"

convert mp4 to mp3

Code

# Define the path to the input MP4 file
input_video_path <- "demo.mp4"  # Replace with the path to your MP4 file

# Define the path to save the output MP3 file
output_audio_path <- "demo.mp3"  # Replace with the desired output path for the MP3 file

# Convert MP4 to MP3
av::av_audio_convert(input_video_path,output_audio_path)

[1] "/Users/jinchaoduan/Documents/Project/Tech-blog/posts/edit video/demo.mp3"

Code

cat("Conversion complete! MP3 saved to:", output_audio_path, "\n")

Conversion complete! MP3 saved to: demo.mp3

Audio

Code

library(av)

Changing length of mp3

Code

video_info=av::av_media_info("demo.mp3" )
video_info$duration

[1] 30.04082

Code

pcm_data <- read_audio_bin("demo.mp3" , channels = 1, end_time = 2.0)
plot(pcm_data, type = 'l')

Code

start_time <- 2 # Start at 1 seconds
total_time <- 4  # Keep for 10 seconds

av_audio_convert(audio="demo.mp3",output="demo_cut.mp3",start_time=start_time,total_time=total_time)

[1] "/Users/jinchaoduan/Documents/Project/Tech-blog/posts/edit video/demo_cut.mp3"

Code

video_info=av::av_media_info("demo_cut.mp3")
video_info$duration

[1] 4.101224

剪切视频/音频

Video

check video resolution

check video length and size

change video resolution

change length of video

video Crop

video to image

convert mp4 to mp3

Audio

Changing length of mp3

convert mp3 to wav