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ChineseVideo Social
视频社交媒体适配
Prepare video for social media platforms: correct aspect ratios, resolutions, bitrates, and container settings.
为社交媒体平台准备视频：调整正确的宽高比、分辨率、比特率和容器设置。
Platform Presets
平台预设
| Platform | Aspect | Max Resolution | Max Duration | Video Bitrate | Audio |
|---|---|---|---|---|---|
| Instagram Feed | 4:5 portrait or 1:1 | 1080×1350 / 1080×1080 | 60s | 3.5 Mbps | AAC 128k |
| Instagram Reels | 9:16 | 1080×1920 | 90s | 8 Mbps | AAC 192k |
| TikTok | 9:16 | 1080×1920 | 10min | 8 Mbps | AAC 192k |
| YouTube Shorts | 9:16 | 1080×1920 | 60s | 8 Mbps | AAC 192k |
| YouTube Standard | 16:9 | 1920×1080 | unlimited | 8 Mbps (1080p) | AAC 192k |
| Twitter / X | 16:9 or 1:1 | 1920×1200 | 140s | 25 Mbps cap | AAC 128k |
| 16:9 or 9:16 | 1920×1080 | 240min | 4 Mbps | AAC 128k | |
| 16:9 | 1920×1080 | 10min | 5 Mbps | AAC 128k |
| 平台 | 宽高比 | 最大分辨率 | 最长时长 | 视频比特率 | 音频 |
|---|---|---|---|---|---|
| Instagram Feed | 4:5竖屏或1:1方形 | 1080×1350 / 1080×1080 | 60秒 | 3.5 Mbps | AAC 128k |
| Instagram Reels | 9:16 | 1080×1920 | 90秒 | 8 Mbps | AAC 192k |
| TikTok | 9:16 | 1080×1920 | 10分钟 | 8 Mbps | AAC 192k |
| YouTube Shorts | 9:16 | 1080×1920 | 60秒 | 8 Mbps | AAC 192k |
| YouTube Standard | 16:9 | 1920×1080 | 无限制 | 8 Mbps（1080p） | AAC 192k |
| Twitter / X | 16:9或1:1 | 1920×1200 | 140秒 | 最高25 Mbps | AAC 128k |
| 16:9或9:16 | 1920×1080 | 240分钟 | 4 Mbps | AAC 128k | |
| 16:9 | 1920×1080 | 10分钟 | 5 Mbps | AAC 192k |
Process
处理流程
1. Identify platform
1. 确定目标平台
If the request is ambiguous (e.g., "make it vertical"), ask which platform — bitrate and audio requirements differ.
如果请求不明确（例如“改成竖屏”），询问具体平台——不同平台的比特率和音频要求不同。
2. Probe source
2. 分析源视频
bash
ffprobe -v quiet -print_format json -show_streams -show_format "$INPUT"Extract: width, height, duration, existing bitrate, audio codec.
bash
ffprobe -v quiet -print_format json -show_streams -show_format "$INPUT"提取信息：宽度、高度、时长、现有比特率、音频编码格式。
3. Determine required transforms
3. 确定所需转换操作
Compare probe output against the platform row in the presets table. Apply only the transforms that are actually needed:
- Aspect ratio mismatch → crop or pad (see Key Decisions for the choice rule)
- Resolution too large → scale down (never upscale; social platforms reject oversized files at upload)
- Duration exceeds platform limit → trim; confirm cut point with user first
- Bitrate over limit → re-encode with target bitrate (platforms reject or silently degrade over-bitrate uploads)
Exit condition: when all four properties (aspect ratio, resolution, duration, bitrate) are within platform bounds and will be set, proceed to Step 4. If source already matches all properties, skip to Step 5 with a simple re-encode plan.
-movflags +faststart将分析结果与预设表格中的平台要求对比。仅执行实际需要的转换：
- 宽高比不匹配 → 裁剪或添加黑边（参考关键决策中的选择规则）
- 分辨率过大 → 缩小分辨率（绝不放大；社交媒体平台会拒绝过大的上传文件）
- 时长超过平台限制 → 剪辑；先与用户确认剪辑位置
- 比特率超过限制 → 重新编码至目标比特率（平台会拒绝或自动降低超比特率的上传文件质量）
退出条件：当宽高比、分辨率、时长、比特率这四个属性均符合平台要求，且将设置时，进入步骤4。如果源视频已符合所有要求，直接跳至步骤5，仅需执行简单的重新编码计划。
-movflags +faststart4. Construct command
4. 构建命令
Crop to fit (preferred when subject is centered):
bash
undefined裁剪适配（当主体居中时优先选择）：
bash
undefined16:9 source → 9:16 (1080×1920), center crop:
16:9源视频 → 9:16（1080×1920），居中裁剪：
ffmpeg -i "$INPUT"
-vf "crop=ih*9/16:ih,scale=1080:1920"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
-vf "crop=ih*9/16:ih,scale=1080:1920"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
**Pad to fit** (preserves full frame, adds letterbox/pillarbox):
```bashffmpeg -i "$INPUT"
-vf "crop=ih*9/16:ih,scale=1080:1920"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
-vf "crop=ih*9/16:ih,scale=1080:1920"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
**添加黑边适配**（保留完整画面，添加上下或左右黑边）：
```bash16:9 source → 9:16 with black bars:
16:9源视频 → 9:16并添加黑边：
ffmpeg -i "$INPUT"
-vf "scale=1080:-2,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
-vf "scale=1080:-2,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
**Square (1:1) from 16:9 — center crop:**
```bash
ffmpeg -i "$INPUT" \
-vf "crop=ih:ih,scale=1080:1080" \
-c:v libx264 -b:v 3500k \
-c:a aac -b:a 128k \
-movflags +faststart "$OUTPUT"ffmpeg -i "$INPUT"
-vf "scale=1080:-2,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
-vf "scale=1080:-2,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black"
-c:v libx264 -b:v 8000k
-c:a aac -b:a 192k
-movflags +faststart "$OUTPUT"
**从16:9裁剪为方形（1:1）——居中裁剪：**
```bash
ffmpeg -i "$INPUT" \
-vf "crop=ih:ih,scale=1080:1080" \
-c:v libx264 -b:v 3500k \
-c:a aac -b:a 128k \
-movflags +faststart "$OUTPUT"5. Confirm
5. 确认方案
State: crop vs. pad choice, any trim, output resolution and bitrate, output path. Wait for approval.
告知用户：裁剪或添加黑边的选择、是否需要剪辑、输出分辨率和比特率、输出路径。等待用户确认。
6. Run and verify
6. 执行并验证
After encoding, verify bitrate:
ffprobe -v quiet -show_format "$OUTPUT" | grep bit_rate编码完成后，验证比特率：
ffprobe -v quiet -show_format "$OUTPUT" | grep bit_rateKey Decisions
关键决策
- Always include — relocates the moov atom to the file start, enabling progressive playback before full download. Required for all social platforms.
-movflags +faststart - Crop vs. pad: default to crop for talking-head or centered subjects; default to pad for wide scenic shots or text-heavy content. When the user says "don't cut anything off", use pad. When uncertain with off-center subjects, ask before running.
- Never upscale: if source is smaller than target resolution, scale to fit within bounds or keep original dimensions.
- 始终添加——将moov原子移至文件开头，支持在完全下载前进行渐进式播放。所有社交媒体平台均要求此项设置。
-movflags +faststart - 裁剪vs添加黑边：默认对访谈类或主体居中的视频进行裁剪；默认对宽幅风景或文字较多的视频添加黑边。当用户要求“不要裁剪任何内容”时，使用添加黑边的方式。若主体偏离中心且不确定时，先询问用户再执行操作。
- 绝不放大：如果源视频分辨率小于目标分辨率，缩放至符合边界或保持原尺寸。