gupsammy/claudest/share-social

Video Social

Prepare video for social media platforms: correct aspect ratios, resolutions, bitrates, and container settings.

Platform Presets

Process

1. Identify platform

If the request is ambiguous (e.g., "make it vertical"), ask which platform — bitrate and audio requirements differ.

2. Probe source

ffprobe -v quiet -print_format json -show_streams -show_format "$INPUT"

Extract: width, height, duration, existing bitrate, audio codec.

3. Determine required transforms

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 -movflags +faststart will be set, proceed to Step 4. If source already matches all properties, skip to Step 5 with a simple re-encode plan.

4. Construct command

Crop to fit (preferred when subject is centered):

# 16:9 source → 9:16 (1080×1920), center crop:
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"

Pad to fit (preserves full frame, adds letterbox/pillarbox):

# 16:9 source → 9:16 with black bars:
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"

Square (1:1) from 16:9 — center crop:

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

State: crop vs. pad choice, any trim, output resolution and bitrate, output path. Wait for approval.

6. Run and verify

After encoding, verify bitrate: ffprobe -v quiet -show_format "$OUTPUT" | grep bit_rate

Key Decisions

• Always include -movflags +faststart — relocates the moov atom to the file start, enabling progressive playback before full download. Required for all social platforms.
• 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.