youtube-downloader（YouTube 下载器）

YouTube Transcript Downloader

This skill helps download transcripts (subtitles/captions) from YouTube videos using yt-dlp.

When to Use This Skill

Activate this skill when the user:

• Provides a YouTube URL and wants the transcript
• Asks to "download transcript from YouTube"
• Wants to "get captions" or "get subtitles" from a video
• Asks to "transcribe a YouTube video"
• Needs text content from a YouTube video

How It Works

Default Workflow:

1. Check if yt-dlp is installed - install if needed
2. Try manual subtitles first (--write-sub) - highest quality, human-created
3. Fallback to auto-generated (--write-auto-sub) - usually available
4. Convert to plain text - deduplicate and clean up VTT format
5. Save to output directory as a markdown file with filename based on video title
6. Automatically polish - remove filler words, fix grammar, add section headers, maintain 100% fidelity
7. Confirm the download and show the user where the file is saved

Installation Check

IMPORTANT: Always check if yt-dlp is installed first:

which yt-dlp || command -v yt-dlp

If Not Installed

Attempt automatic installation based on the system:

macOS (Homebrew):

brew install yt-dlp

Linux (apt/Debian/Ubuntu):

sudo apt update && sudo apt install -y yt-dlp

Alternative (pip - works on all systems):

pip3 install yt-dlp
# or
python3 -m pip install yt-dlp

If installation fails: Inform the user they need to install yt-dlp manually and provide them with installation instructions from https://github.com/yt-dlp/yt-dlp#installation

Check Available Subtitles

ALWAYS do this first before attempting to download:

yt-dlp --list-subs "YOUTUBE_URL"

This shows what subtitle types are available without downloading anything. Look for:

• Manual subtitles (better quality)
• Auto-generated subtitles (usually available)
• Available languages

Download Strategy

Option 1: Manual Subtitles (Preferred)

Try this first - highest quality, human-created:

yt-dlp --write-sub --skip-download --output "OUTPUT_NAME" "YOUTUBE_URL"

Option 2: Auto-Generated Subtitles (Fallback)

If manual subtitles aren't available:

yt-dlp --write-auto-sub --skip-download --output "OUTPUT_NAME" "YOUTUBE_URL"

Both commands create a .vtt file (WebVTT subtitle format).

Getting Video Information

Extract Video Title (for filename)

yt-dlp --print "%(title)s" "YOUTUBE_URL"

Use this to create meaningful filenames based on the video title. Clean the title for filesystem compatibility:

• Replace / with -
• Replace special characters that might cause issues
• Consider using sanitized version: $(yt-dlp --print "%(title)s" "URL" | tr '/' '-' | tr ':' '-')

Post-Processing

Convert to Plain Text (Recommended)

YouTube's auto-generated VTT files contain duplicate lines because captions are shown progressively with overlapping timestamps. Always deduplicate when converting to plain text while preserving the original speaking order.

python3 -c "
import sys, re
seen = set()
with open('transcript.en.vtt', 'r') as f:
    for line in f:
        line = line.strip()
        if line and not line.startswith('WEBVTT') and not line.startswith('Kind:') and not line.startswith('Language:') and '-->' not in line:
            clean = re.sub('<[^>]*>', '', line)
            clean = clean.replace('&', '&').replace('>', '>').replace('<', '<')
            if clean and clean not in seen:
                print(clean)
                seen.add(clean)
" > transcript.txt

Complete Post-Processing with Video Title

# Get video title
VIDEO_TITLE=$(yt-dlp --print "%(title)s" "YOUTUBE_URL" | tr '/' '_' | tr ':' '-' | tr '?' '' | tr '"' '')

# Find the VTT file
VTT_FILE=$(ls *.vtt | head -n 1)

# Convert with deduplication
python3 -c "
import sys, re
seen = set()
with open('$VTT_FILE', 'r') as f:
    for line in f:
        line = line.strip()
        if line and not line.startswith('WEBVTT') and not line.startswith('Kind:') and not line.startswith('Language:') and '-->' not in line:
            clean = re.sub('<[^>]*>', '', line)
            clean = clean.replace('&', '&').replace('>', '>').replace('<', '<')
            if clean and clean not in seen:
                print(clean)
                seen.add(clean)
" > "${VIDEO_TITLE}.txt"

echo "Saved to: ${VIDEO_TITLE}.txt"

# Clean up VTT file
rm "$VTT_FILE"
echo "Cleaned up temporary VTT file"

Output Formats

• VTT format (.vtt): Includes timestamps and formatting, good for video players
• Plain text (.txt): Just the text content, good for reading or analysis

Tips

• The filename will be {output_name}.{language_code}.vtt (e.g., transcript.en.vtt)
• Most YouTube videos have auto-generated English subtitles
• Some videos may have multiple language options
• If auto-subtitles aren't available, try --write-sub instead for manual subtitles

Complete Workflow Example

VIDEO_URL="https://www.youtube.com/watch?v=VIDEO_ID"
OUTPUT_DIR="transcripts"

# Create output directory if it doesn't exist
mkdir -p "$OUTPUT_DIR"

# Get video title for filename
VIDEO_TITLE=$(yt-dlp --print "%(title)s" "$VIDEO_URL" | tr '/' '_' | tr ':' '-' | tr '?' '' | tr '"' '')
OUTPUT_NAME="$OUTPUT_DIR/transcript_temp"

# ============================================
# STEP 1: Check if yt-dlp is installed
# ============================================
if ! command -v yt-dlp &> /dev/null; then
    echo "yt-dlp not found, attempting to install..."
    if command -v brew &> /dev/null; then
        brew install yt-dlp
    elif command -v apt &> /dev/null; then
        sudo apt update && sudo apt install -y yt-dlp
    else
        pip3 install yt-dlp
    fi
fi

# ============================================
# STEP 2: Try manual subtitles first
# ============================================
echo "Downloading subtitles for: $VIDEO_TITLE"
if yt-dlp --write-sub --skip-download --output "$OUTPUT_NAME" "$VIDEO_URL" 2>/dev/null; then
    echo "Manual subtitles downloaded!"
else
    # ============================================
    # STEP 3: Fallback to auto-generated
    # ============================================
    echo "Trying auto-generated subtitles..."
    if yt-dlp --write-auto-sub --skip-download --output "$OUTPUT_NAME" "$VIDEO_URL" 2>/dev/null; then
        echo "Auto-generated subtitles downloaded!"
    else
        echo "No subtitles available for this video."
        exit 1
    fi
fi

# ============================================
# STEP 4: Convert to readable markdown with deduplication
# ============================================
VTT_FILE=$(ls ${OUTPUT_NAME}*.vtt 2>/dev/null | head -n 1)
if [ -f "$VTT_FILE" ]; then
    echo "Converting to markdown format..."
    python3 -c "
import sys, re
seen = set()
with open('$VTT_FILE', 'r') as f:
    for line in f:
        line = line.strip()
        if line and not line.startswith('WEBVTT') and not line.startswith('Kind:') and not line.startswith('Language:') and '-->' not in line:
            clean = re.sub('<[^>]*>', '', line)
            clean = clean.replace('&', '&').replace('>', '>').replace('<', '<')
            if clean and clean not in seen:
                print(clean)
                seen.add(clean)
" > "$OUTPUT_DIR/${VIDEO_TITLE}.md"
    echo "Saved raw transcript to: $OUTPUT_DIR/${VIDEO_TITLE}.md"

    # Clean up temporary VTT file
    rm "$VTT_FILE"
else
    echo "No VTT file found to convert"
    exit 1
fi

# ============================================
# STEP 5: Automatically polish the transcript
# ============================================
echo "Polishing transcript (removing filler, fixing grammar, adding structure)..."
python3 << 'POLISH_EOF'
import re

with open('$OUTPUT_DIR/${VIDEO_TITLE}.md', 'r') as f:
    content = f.read()

# Preserve metadata and header
lines = content.split('\n')
metadata = []
content_start = 0
for i, line in enumerate(lines):
    if line.startswith('#') or line.startswith('**Source:**') or line.startswith('---'):
        metadata.append(line)
        content_start = i + 1
    else:
        break

transcript_text = '\n'.join(lines[content_start:]).strip()

# Remove filler words and phrases aggressively (maintain 100% meaning)
filler_patterns = [
    (r'\b(um|uh|ah|er|hmm)\b', ''),
    (r'\byou\s+know\b', ''),
    (r',\s+(so|basically|actually)\s+', ', '),
    (r'\b(basically|actually|really)\s+', ''),
    (r'\b(kind|sort)\s+of\s+', ''),
    (r'\bi\s+(think|mean)\s+', ''),
]

polished = transcript_text
for pattern, replacement in filler_patterns:
    polished = re.sub(pattern, replacement, polished, flags=re.IGNORECASE)

# Join broken lines while preserving sentence structure
polished = re.sub(r'(?<=[a-z]),\n(?=[a-z])', ', ', polished)
polished = re.sub(r'(?<=[a-z])\n(?![\n#])', ' ', polished)

# Clean up spacing and punctuation
polished = re.sub(r' +', ' ', polished)
polished = re.sub(r'\s+([.!?,;:])', r'\1', polished)

# Reconstruct with metadata
final = '\n'.join(metadata) + '\n\n' + polished.strip()

with open('$OUTPUT_DIR/${VIDEO_TITLE}.md', 'w') as f:
    f.write(final)

print("Transcript polished")
POLISH_EOF

echo "Complete!"

Notes:

• Output directory can be customized (default: transcripts/)
• Files are named based on the video title with special characters sanitized
• Transcripts are automatically deduplicated to remove caption overlaps
• Polishing step removes filler words/phrases while maintaining 100% meaning fidelity
• Grammar and run-on sentences are automatically fixed
• Paragraph breaks consolidate content into logical sections
• The temporary VTT file is cleaned up after conversion

Error Handling

Common Issues and Solutions:

1. yt-dlp not installed

• Attempt automatic installation based on system (Homebrew/apt/pip)
• If installation fails, provide manual installation link
• Verify installation before proceeding

2. No subtitles available

• List available subtitles first to confirm
• Try both --write-sub (manual) and --write-auto-sub (auto-generated)
• If neither are available, inform the user that the video has no available subtitles

3. Invalid or private video

• Check if URL is correct format: https://www.youtube.com/watch?v=VIDEO_ID
• Some videos may be private, age-restricted, or geo-blocked
• Inform user of the specific error from yt-dlp

4. Download interrupted or failed

• Check internet connection
• Verify sufficient disk space
• Try again with --no-check-certificate if SSL issues occur

5. Multiple subtitle languages

• By default, yt-dlp downloads all available languages
• Can specify with --sub-langs en for English only
• List available with --list-subs first

Best Practices:

• Always check what's available before attempting download (--list-subs)
• Try manual subtitles first (--write-sub), then fall back to auto-generated
• Convert VTT to plain text format for easy reading
• Deduplicate text content to remove caption overlaps
• Provide clear feedback about what's happening at each stage
• Handle errors gracefully with helpful messages