How to use FFmpeg for batch processing and automation tasks? - 面试题

FFmpeg can achieve batch processing through scripts and tools, greatly improving work efficiency, suitable for processing large numbers of video files.

Basic Batch Processing

Batch Transcoding Using Shell Scripts

bash
#!/bin/bash

# Batch transcode MP4 files
for file in *.mp4; do
    output="output_${file}"
    ffmpeg -i "$file" -c:v libx264 -crf 23 -c:a aac -b:a 128k "$output"
done

# Batch convert formats
for file in *.avi; do
    output="${file%.avi}.mp4"
    ffmpeg -i "$file" -c:v libx264 -crf 23 -c:a aac -b:a 128k "$output"
done

Batch Processing Using find Command

bash
# Recursively process all videos in directory
find input_dir -name "*.mp4" -exec ffmpeg -i {} -c:v libx264 -crf 23 output_dir/{} \;

# Batch extract audio
find input_dir -name "*.mp4" -exec ffmpeg -i {} -vn -c:a copy output_dir/{/.}.aac \;

Parallel Processing

Using GNU Parallel

bash
# Install GNU Parallel
brew install parallel  # macOS
apt-get install parallel  # Ubuntu/Debian

# Process 4 files in parallel
find input_dir -name "*.mp4" | parallel -j 4 ffmpeg -i {} -c:v libx264 -crf 23 output_dir/{/.}.mp4

# Show progress
find input_dir -name "*.mp4" | parallel --bar -j 4 ffmpeg -i {} -c:v libx264 -crf 23 output_dir/{/.}.mp4

Parallel Processing Using xargs

bash
# Process 4 files in parallel
find input_dir -name "*.mp4" | xargs -P 4 -I {} ffmpeg -i {} -c:v libx264 -crf 23 output_dir/{/.}.mp4

Python Batch Processing

Using subprocess Module

python
import subprocess
import os
import glob

# Batch transcode videos
input_dir = "input"
output_dir = "output"
os.makedirs(output_dir, exist_ok=True)

for input_file in glob.glob(f"{input_dir}/*.mp4"):
    filename = os.path.basename(input_file)
    output_file = os.path.join(output_dir, f"converted_{filename}")
    
    cmd = [
        "ffmpeg", "-i", input_file,
        "-c:v", "libx264", "-crf", "23",
        "-c:a", "aac", "-b:a", "128k",
        output_file
    ]
    
    subprocess.run(cmd, check=True)
    print(f"Processed: {filename}")

Parallel Processing Using multiprocessing

python
import subprocess
import os
import glob
from multiprocessing import Pool

def process_video(input_file):
    output_dir = "output"
    filename = os.path.basename(input_file)
    output_file = os.path.join(output_dir, f"converted_{filename}")
    
    cmd = [
        "ffmpeg", "-i", input_file,
        "-c:v", "libx264", "-crf", "23",
        "-c:a", "aac", "-b:a", "128k",
        output_file
    ]
    
    subprocess.run(cmd, check=True)
    return filename

# Parallel processing
input_files = glob.glob("input/*.mp4")
with Pool(processes=4) as pool:
    results = pool.map(process_video, input_files)
    for result in results:
        print(f"Processed: {result}")

PowerShell Batch Processing

Windows PowerShell Script

powershell
# Batch transcode videos
$inputDir = "input"
$outputDir = "output"
New-Item -ItemType Directory -Force -Path $outputDir

Get-ChildItem -Path $inputDir -Filter "*.mp4" | ForEach-Object {
    $inputFile = $_.FullName
    $outputFile = Join-Path $outputDir "converted_$($_.Name)"
    
    ffmpeg -i $inputFile -c:v libx264 -crf 23 -c:a aac -b:a 128k $outputFile
    Write-Host "Processed: $($_.Name)"
}

Advanced Batch Processing

Adjust Parameters Based on File Size

bash
#!/bin/bash

for file in *.mp4; do
    size=$(stat -f%z "$file" 2>/dev/null || stat -c%s "$file")
    size_mb=$((size / 1024 / 1024))
    
    if [ $size_mb -gt 100 ]; then
        # Large files use higher compression
        ffmpeg -i "$file" -c:v libx264 -crf 28 -preset slow "compressed_$file"
    else
        # Small files use default parameters
        ffmpeg -i "$file" -c:v libx264 -crf 23 -preset medium "compressed_$file"
    fi
done

Adjust Parameters Based on Resolution

bash
#!/bin/bash

for file in *.mp4; do
    # Get video resolution
    resolution=$(ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 "$file")
    
    if [[ $resolution == "1920x1080" ]]; then
        # 1080p video downscale to 720p
        ffmpeg -i "$file" -vf scale=1280:720 -c:v libx264 -crf 23 "720p_$file"
    elif [[ $resolution == "3840x2160" ]]; then
        # 4K video downscale to 1080p
        ffmpeg -i "$file" -vf scale=1920:1080 -c:v libx264 -crf 23 "1080p_$file"
    else
        # Other resolutions remain unchanged
        ffmpeg -i "$file" -c:v libx264 -crf 23 "compressed_$file"
    fi
done

Batch Generate Thumbnails

bash
#!/bin/bash

for file in *.mp4; do
    filename="${file%.*}"
    # Capture thumbnail at 10%
    ffmpeg -i "$file" -ss 00:00:05 -vframes 1 -vf scale=320:180 "${filename}_thumb.jpg"
    echo "Generated thumbnail for: $file"
done

Error Handling and Logging

Batch Processing with Error Handling

bash
#!/bin/bash

log_file="processing.log"
error_count=0

for file in *.mp4; do
    echo "Processing: $file" | tee -a "$log_file"
    
    if ffmpeg -i "$file" -c:v libx264 -crf 23 "output_$file" 2>> "$log_file"; then
        echo "Success: $file" | tee -a "$log_file"
    else
        echo "Error: $file" | tee -a "$log_file"
        ((error_count++))
    fi
done

echo "Total errors: $error_count" | tee -a "$log_file"

Python with Error Handling

python
import subprocess
import os
import glob
import logging

logging.basicConfig(filename='processing.log', level=logging.INFO)

def process_video(input_file):
    try:
        output_file = f"output_{os.path.basename(input_file)}"
        cmd = ["ffmpeg", "-i", input_file, "-c:v", "libx264", "-crf", "23", output_file]
        subprocess.run(cmd, check=True, capture_output=True)
        logging.info(f"Success: {input_file}")
        return True
    except subprocess.CalledProcessError as e:
        logging.error(f"Error: {input_file} - {e.stderr.decode()}")
        return False

# Batch processing
input_files = glob.glob("*.mp4")
success_count = sum(process_video(f) for f in input_files)
error_count = len(input_files) - success_count

logging.info(f"Total: {len(input_files)}, Success: {success_count}, Errors: {error_count}")

Automated Tasks

Scheduled Tasks (Cron)

bash
# Add to crontab
# Execute batch processing at 2 AM every day
0 2 * * * /path/to/batch_process.sh >> /var/log/ffmpeg_batch.log 2>&1

Monitor Directory for Automatic Processing

python
import time
import os
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler

class VideoHandler(FileSystemEventHandler):
    def on_created(self, event):
        if event.src_path.endswith('.mp4'):
            print(f"New video detected: {event.src_path}")
            process_video(event.src_path)

def process_video(input_file):
    output_file = f"output_{os.path.basename(input_file)}"
    cmd = ["ffmpeg", "-i", input_file, "-c:v", "libx264", "-crf", "23", output_file]
    subprocess.run(cmd)

if __name__ == "__main__":
    event_handler = VideoHandler()
    observer = Observer()
    observer.schedule(event_handler, path='input_dir', recursive=False)
    observer.start()
    
    try:
        while True:
            time.sleep(1)
    except KeyboardInterrupt:
        observer.stop()
    observer.join()

Batch Processing Best Practices

Use parallel processing: Fully utilize multi-core CPUs to improve processing speed
Add error handling: Log errors for troubleshooting
Monitor resource usage: Avoid processing too many files simultaneously to prevent system resource exhaustion
Test small batches: Test small batches before large-scale processing
Use progress display: Understand processing progress to estimate completion time
Backup original files: Backup important files before processing

Batch processing can significantly improve work efficiency, but pay attention to system resource management and error handling.