LinkedIn video ad specs: 16:9, 1:1, 4:5, 9:16 and the 30-second loop

LinkedIn's video ad page lists 16:9 (1920x1080 recommended), 1:1, 4:5 at 720x900 and 9:16 at 720x1280, MP4 only, 3 seconds to 30 minutes, 75 KB to 500 MB, and under 30 FPS. It also says a video shorter than 30 seconds loops until 30 seconds of playback. Read 2026-09-29.

What does LinkedIn list?

Codec is H.264 or VP8; audio is AAC or MPEG4. Captions are supported as SRT files. LinkedIn recommends 15 to 30 seconds. In-stream placements run up to 90 seconds.

How do I generate each ratio?

16:9, 1:1 and 9:16 are all in the aspect_ratio list of seedance-2.5, wan-3.0 and kling-3. None of the video models lists 4:5. For a 4:5 ad, generate 1:1 or 9:16 and crop with POST /v1/video-filter (a crop op with fractional x, y, width, height; $0.02 per job), or size a Timeline output of 720x900 (even integers in 256 to 2160).

Timeline fps is 24, 25, 30 or 60, so choose 24 or 25 to stay under 30 FPS.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: linkedin-45-001" \
  -d '{
    "audio": {
      "url": "https://media.sume.com/artifacts/artf_demo/voice.wav",
      "duration_seconds": 24
    },
    "video": [
      { "source_url": "https://media.sume.com/artifacts/artf_demo/a.mp4", "start": 0, "duration": 12 },
      { "source_url": "https://media.sume.com/artifacts/artf_demo/b.mp4", "start": 12, "duration": 12 }
    ],
    "output": { "width": 720, "height": 900, "fps": 25 }
  }'

What about the loop and captions?

The 30-second loop rule is LinkedIn's; a 12-second clip will repeat. Design a clean loop point. LinkedIn takes captions as SRT, but Sume does not accept or output SRT. Its captions are burned in with POST /v1/video-captions, so use that route instead and skip LinkedIn's separate file.

What are the limits of this answer?

Sume's docs say callers do not choose the codec. Check the file against the page before you upload.