add 2026-02-03-ffmpeg-select-frames

Signed-off-by: code4lala <fenglala@outlook.com>

Author: code4lala

_posts/2026-02-03-ffmpeg-select-frames.markdown

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+---
+layout: post
+comments: true
+title:  "使用ffmpeg裁剪想要的帧"
+date:   2026-02-03 21:33:26 +0800
+tags: ffmpeg
+lang: zh
+---
+
+`原创`
+
+看到 https://www.youtube.com/watch?v=zzHeG7l6FT8 《【東方ボーカルMV】東方言えるかな》里有非常多漂亮的角色（我全都要），觉得很适合拿来做壁纸用，但是又有一些没有画面的场景，可以剪掉来提升观感。
+
+成品链接：
+https://steamcommunity.com/sharedfiles/filedetails/?id=3659280460
+
+在线观看：
+https://www.bilibili.com/video/BV1HGFLz8E1H
+
+### 步骤：
+
+1. 从youtube上下载视频和音频
+2. 使用ffmpeg合并视频和音频
+3. 使用ffmpeg导出所有帧为图片
+4. 人工过一遍所有图片，把没有人物的场景删掉
+5. 整理出来筛选后的图片帧序号并使用ffmpeg裁剪视频
+
+### 从youtube上下载视频和音频
+
+第一步这里使用  
+https://snapany.com/zh/youtube-1  
+直接解析youtube地址拿到googlevideo.com域名的链接来下载。  
+这里下载到的视频和音频是两个独立的文件。
+
+### 使用ffmpeg合并视频和音频
+
+让AI生成一个ffmpeg命令
+
+```sh
+ffmpeg -i videoplayback.mp4 -i videoplayback.m4a -c copy output.mp4
+```
+
+### 使用ffmpeg导出所有帧为图片
+
+让AI生成一个ffmpeg命令
+
+```sh
+ffmpeg -i input.mp4 frame_%05d.png
+```
+
+这里我导出了之后复制一份，一份是原始的，一份用来人工筛选后删除不需要的，方便后续剪视频。
+
+### 让AI整理出来筛选后的图片帧序号并使用ffmpeg裁剪视频
+
+直接让AI写个python脚本
+
+```python
+import os
+import re
+import subprocess
+
+def find_deleted_ranges(images_dir, images2_dir):
+    all_frames = []
+    for f in os.listdir(images2_dir):
+        m = re.match(r"frame_(\d+)\.png", f)
+        if m:
+            all_frames.append(int(m.group(1)))
+    all_frames.sort()
+
+    keep_frames = []
+    for f in os.listdir(images_dir):
+        m = re.match(r"frame_(\d+)\.png", f)
+        if m:
+            keep_frames.append(int(m.group(1)))
+    keep_frames.sort()
+
+    keep_set = set(keep_frames)
+    deleted = [n for n in all_frames if n not in keep_set]
+
+    print("\n===== 帧统计 =====")
+    print(f"原视频总帧数: {len(all_frames)}")
+    print(f"保留帧数: {len(keep_frames)}")
+    print(f"删除帧数: {len(deleted)}")
+
+    if not deleted:
+        return [], all_frames, keep_frames, deleted
+
+    ranges = []
+    start = deleted[0]
+    prev = deleted[0]
+
+    for n in deleted[1:]:
+        if n == prev + 1:
+            prev = n
+        else:
+            ranges.append((start, prev))
+            start = n
+            prev = n
+    ranges.append((start, prev))
+
+    print("\n===== 删除的连续帧区间 =====")
+    for s, e in ranges:
+        print(f"  - 从 {s} 到 {e} （共 {e - s + 1} 帧）")
+
+    return ranges, all_frames, keep_frames, deleted
+
+
+def build_video_select(ranges):
+    parts = []
+    for s, e in ranges:
+        parts.append(f"between(n,{s-1},{e-1})")
+    return "not(" + "+".join(parts) + ")"
+
+
+def build_audio_select(ranges, fps):
+    parts = []
+    for s, e in ranges:
+        t1 = (s - 1) / fps
+        t2 = (e - 1) / fps
+        parts.append(f"between(t,{t1},{t2})")
+    return "not(" + "+".join(parts) + ")"
+
+
+def get_fps(ffmpeg, input_video):
+    cmd = [ffmpeg, "-i", input_video]
+    p = subprocess.Popen(cmd, stderr=subprocess.PIPE, stdout=subprocess.PIPE, text=True)
+    out, err = p.communicate()
+    fps_match = re.search(r"(\d+(?:\.\d+)?) fps", err)
+    fps = float(fps_match.group(1)) if fps_match else 30.0
+    print("\n原视频帧率 =", fps)
+    return fps
+
+
+def get_frame_count(ffprobe, video_path):
+    cmd = [
+        ffprobe,
+        "-v", "error",
+        "-select_streams", "v:0",
+        "-count_packets",
+        "-show_entries", "stream=nb_read_packets",
+        "-of", "csv=p=0",
+        video_path
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True)
+    try:
+        return int(result.stdout.strip())
+    except:
+        return None
+
+
+def main():
+    ffmpeg = r".\ffmpeg-2026-01-29-git-c898ddb8fe-full_build\bin\ffmpeg.exe"
+    ffprobe = r".\ffmpeg-2026-01-29-git-c898ddb8fe-full_build\bin\ffprobe.exe"
+
+    input_video = "videoplayback.mp4"
+    output_video = "video_cut.mp4"
+
+    images_dir = "images" # 这个是删过帧只保留了人物画面的文件夹
+    images2_dir = "images2" # 这个是原始的所有帧的文件夹
+
+    ranges, all_frames, keep_frames, deleted = find_deleted_ranges(images_dir, images2_dir)
+    if not ranges:
+        return
+
+    fps = get_fps(ffmpeg, input_video)
+
+    video_select = build_video_select(ranges)
+    audio_select = build_audio_select(ranges, fps)
+
+    print("\n===== 视频过滤表达式 =====")
+    print(video_select)
+
+    print("\n===== 音频过滤表达式（按时间） =====")
+    print(audio_select)
+
+    cmd = [
+        ffmpeg,
+        "-i", input_video,
+        "-vf", f"select='{video_select}',setpts=N/({fps}*TB)",
+        "-af", f"aselect='{audio_select}',asetpts=N/SR/TB",
+        "-c:v", "libx264",
+        "-c:a", "aac",
+        "-pix_fmt", "yuv420p",
+        "-y",
+        output_video
+    ]
+
+    print("\n===== 开始裁剪视频（含音频） =====")
+    subprocess.run(cmd)
+    print("\n完成！输出文件：", output_video)
+
+    actual_frames = get_frame_count(ffprobe, output_video)
+
+    print("\n===== 裁剪后帧数验证 =====")
+    print(f"预期保留帧数: {len(keep_frames)}")
+    print(f"实际视频帧数: {actual_frames}")
+
+    if actual_frames == len(keep_frames):
+        print("✔ 帧数完全一致，音视频同步裁剪成功")
+    else:
+        print("✘ 帧数不一致，请检查源数据")
+
+
+if __name__ == "__main__":
+    main()
+```