Deliver a landscape clip on a vertical letterbox canvas

01Prepare environment and inputs

1. Prepare Node.js and FFmpeg with libx264, scale and pad available; set FFMPEG_BIN when necessary. The recorded environment was Node v24.18.0 and FFmpeg 6.0.
2. Use the supplied original one-second landscape-source.mp4. It has ten frames, a red left edge and a yellow right edge, and intentionally contains no audio.
3. Keep the chosen delivery geometry explicit: source 320×180, scaled content 160×90, output 180×320, placement x=10 and y=115. The example uses yuv444p for its small lossless comparison.

02Run the recipe

Run command

node run-recipe.mjs --out ./my-run

1. Establish composition markers

   The script makes the landscape fixture with visible markers on both source edges. Those markers are acceptance targets: losing either edge during conversion would remove source composition, even if the result still has a valid portrait dimension.

2. Scale proportionally and add a canvas

   Apply scale=160:90:flags=neighbor,pad=180:320:10:115:color=black,setsar=1. The 160×90 rectangle preserves 16:9 exactly; the outer canvas is 9:16. Its small side margins deliberately avoid rounding the landscape content to a distorted 180-pixel width.

3. Decode and compare the content rectangle

   Fully decode the exported file into RGB. Compare its 160×90 interior against an independently scaled source frame, using a maximum channel difference tolerance of four. The recorded fixture measured zero. This tolerance and yuv444p fixture are not a general colour-management qualification.

4. Audit borders and frame count

   Check ten output frames, black top and bottom padding, a red left marker and a yellow right marker. The negative case is a local arithmetic aspect-ratio guard: the deliberately unequal cross-products reject stretching. It does not encode a stretched bad file or exercise a general product validator. Keep the measured offsets and actual max RGB difference in the receipt.

03Check the result

• The actual output fully decodes to ten 180×320 RGB frames.
• The outer canvas is 9:16 and the inner 160×90 rectangle remains 16:9.
• The decoded interior differs by at most four channel values from the separately scaled source; the recorded run measured zero.
• Top and bottom sampled padding pixels are black within three channel values.
• The red left and yellow right composition markers remain inside the delivered picture.
• The local arithmetic guard rejects unequal aspect-ratio cross-products; it is not a test of a stretched FFmpeg output. All eight checks pass.

04Troubleshoot and deliver

The measured file proves this layout conversion on the original tiny fixture. Confirm a distribution platform’s codec and resolution requirements separately before using the same geometry for a final upload.

05Download scripts and fixtures

• Original task-specific local-fixture diagram ↓
• Complete runnable kit with original inputs and real receipts ↓
• Task-specific standard-library fixture runner ↓
• Bounded local execution and receipt helpers ↓
• English execution and acceptance guide ↓
• English machine-readable task brief ↓
• Chinese execution and acceptance guide ↓
• Chinese machine-readable task brief ↓
• Actual complete passing execution receipt ↓
• Actual expected-rejection receipt ↓
• Named task-specific check results ↓
• SHA-256 inventory for distributed files ↓
• Recorded fixture: landscape-source.mp4 ↓
• Recorded fixture: vertical-letterbox.mp4 ↓