video-subtitles-and-audio-insert-workflow

1. Choosing a Technical Approach

Recommended: Python moviepy + CJK fonts

• Tools: moviepy 2.x
• Fonts: System CJK fonts (e.g. STHeiti, Songti, PingFang)
• Pros: Cross-platform, supports Chinese, easy styling control
• Cons: Slower processing (~40s for an 80s video)

Alternative: FFmpeg + libass (requires rebuild)

• Tools: FFmpeg with libass support
• Pros: Fast processing
• Cons: Requires rebuilding FFmpeg; complex setup

2. Core Code Template

#!/usr/bin/env python3
import re
from moviepy import VideoFileClip, TextClip, CompositeVideoClip

def parse_srt(srt_file):
    """Parse an SRT subtitle file."""
    with open(srt_file, 'r', encoding='utf-8') as f:
        content = f.read()
    
    blocks = content.strip().split('\n\n')
    subtitles = []
    
    for block in blocks:
        lines = block.strip().split('\n')
        if len(lines) >= 3:
            time_line = lines[1]
            match = re.match(r'(\d{2}):(\d{2}):(\d{2}),(\d{3}) --> (\d{2}):(\d{2}):(\d{2}),(\d{3})', time_line)
            if match:
                start_h, start_m, start_s, start_ms, end_h, end_m, end_s, end_ms = match.groups()
                start_time = int(start_h) * 3600 + int(start_m) * 60 + int(start_s) + int(start_ms) / 1000
                end_time = int(end_h) * 3600 + int(end_m) * 60 + int(end_s) + int(end_ms) / 1000
                text = '\n'.join(lines[2:])
                subtitles.append(((start_time, end_time), text))
    
    return subtitles

def make_textclip(txt, font_path, font_size=40):
    """Create a subtitle text clip."""
    return TextClip(
        text=txt,
        font_size=font_size,             # Tune for resolution
        color='white',
        font=font_path,                  # CJK-capable font path
        stroke_color='black',
        stroke_width=2.5,
        method='caption',
        size=(1100, None),               # 1100px width, auto height
        text_align='center'
    )

def add_subtitles(video_path, srt_path, output_path, font_path, font_size=40, bottom_margin=100):
    """Burn hard subtitles into a video."""
    video = VideoFileClip(video_path)
    subtitles = parse_srt(srt_path)
    
    subtitle_clips = []
    for (start, end), text in subtitles:
        txt_clip = make_textclip(text, font_path, font_size)
        txt_clip = txt_clip.with_start(start).with_end(end)
        # Position: pixels from bottom (avoids wrapped lines past the lower edge)
        txt_clip = txt_clip.with_position(('center', video.h - bottom_margin))
        subtitle_clips.append(txt_clip)
    
    final_video = CompositeVideoClip([video] + subtitle_clips)
    
    # Important: cap bitrate to avoid huge files
    # Prefer checking source bitrate first, then ~1.2–1.5× that value
    final_video.write_videofile(
        output_path,
        codec='libx264',
        audio_codec='aac',
        fps=video.fps,
        preset='medium',
        bitrate='600k',      # Tune to source (often 400–800k)
        threads=4
    )
    
    video.close()

# Example usage
if __name__ == '__main__':
    add_subtitles(
        video_path='input_video.mp4',
        srt_path='subtitles.srt',
        output_path='output_video_with_subtitles.mp4',
        font_path='/System/Library/Fonts/STHeiti Medium.ttc',  # macOS
        font_size=40,        # e.g. 40px for 1280×720
        bottom_margin=100    # 100px from bottom
    )