Video Social

Platform Presets

Process

1. Identify platform

2. Probe source

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

3. Determine required transforms

• 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)

-movflags +faststart

4. Construct command

# 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"

# 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"

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

6. Run and verify

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.