NoCloud Media

Video tool

Video Aspect Ratio Converter — 9:16, 1:1, 4:5, 16:9

Drop a horizontal phone clip, get a 9:16 TikTok-ready MP4. Drop a vertical clip, get a 16:9 YouTube version. Crop, letterbox, or blurred-background fill — all in your browser, no upload, no watermark.

How it works

  1. 1

    Drop your video

    MP4, MOV, WebM, MKV, AVI, or M4V. Stays on your device.

  2. 2

    Pick the target ratio

    **9:16** for TikTok / Reels / Shorts (1080×1920). **1:1** for Instagram square posts and Facebook ads (1080×1080). **4:5** for Instagram portrait posts (1080×1350) — Instagram's preferred non-Reel format because it occupies the most feed real-estate per scroll. **16:9** for YouTube horizontal and screen recordings (1920×1080).

  3. 3

    Pick a fill mode

    **Blurred background** (default, the user-pleasing one) — fits the video on top of a blurred-and-zoomed copy of itself. Same look CapCut and InShot ship for free-but-watermarked. **Crop** — fills the frame exactly, no bars; pair with the position slider to keep the subject in shot. **Letterbox** — fits everything, adds black bars on the empty axis. Loses no pixels but shows up small on social.

  4. 4

    Position the crop (when in crop mode)

    If your subject isn't centered, drag the slider. For landscape → vertical it slides left/right; for vertical → landscape it slides up/down. The slider goes -1 (far left/top) to +1 (far right/bottom), 0 (center) is the default.

  5. 5

    Convert in your browser

    FFmpeg.wasm crops, scales, pads, and re-encodes to H.264 + AAC, MP4 with faststart. Output lands at 1080 on the longer axis (1080×1920 / 1080×1080 / 1080×1350 / 1920×1080) — matches the canonical sizes TikTok / Instagram / YouTube expect.

  6. 6

    Download the converted MP4

    Ready to upload. Filename includes the new ratio so you can keep multiple variants of the same source side-by-side.

Why use Aspect ratio converter?

Same one-click flow CapCut Pro / Veed / Kapwing charge for. The conversion that turns horizontal phone footage into TikTok-ready vertical (or the inverse for YouTube re-uploads) is the single most-paywalled feature in social-video editing — here it's free and runs locally.

Three fill modes, including the **TikTok / CapCut signature blurred-background** look (FFmpeg `boxblur` on a duplicated zoomed-to-fill stream). Most free converters give you only crop or only letterbox. Pick the right one for your subject.

Position slider for crop mode — slide horizontally for landscape→vertical, vertically for vertical→landscape. Keeps off-center subjects in shot. Veed and Kapwing call this 'Smart Crop' and gate it behind paid tiers; we expose the same FFmpeg primitive.

Output at 1080 on the longer axis matches what social platforms actually expect (TikTok = 1080×1920, Instagram square = 1080×1080, IG portrait = 1080×1350, YouTube = 1920×1080). No more 'why did the platform recompress my upload to 480p' surprises from picking the wrong output size.

Private — your video stays on your device. Useful when re-purposing client work or pre-release content across platforms.

No watermark, no sign-up, no per-clip cap.

Common use cases

  • Convert a horizontal phone video to 9:16 vertical for TikTok / Reels / Shorts (blurred-background fill keeps it cinematic)
  • Re-purpose a vertical phone clip to 16:9 horizontal for YouTube upload (crop with position slider keeps the subject in shot)
  • Repost a 16:9 podcast clip to Instagram 1:1 square or 4:5 portrait for the in-feed scroll
  • Convert a 16:9 product demo to 9:16 vertical for Instagram Reels with the subject reframed via crop position
  • Turn a screen recording into Instagram 4:5 with letterbox bars (no detail lost)
  • Convert vertical phone footage into 16:9 with a blurred-bg fill — cinematic without losing the subject
  • Generate multiple platform variants of the same video (drop, convert, save, drop the same file again with a different ratio)
  • Re-format an old 4:3 home video to 9:16 vertical for nostalgic-style TikTok edits

About MP4 and MP4

Aspect ratio mismatch is the most-common reason someone uses CapCut / Veed / Kapwing. Phone cameras shoot 16:9 horizontal or 9:16 vertical depending on orientation; the platform you're posting to expects something specific (TikTok wants 9:16, YouTube wants 16:9, Instagram square = 1:1, Instagram portrait = 4:5). NoCloud Media uses three FFmpeg strategies depending on what you pick. **Crop mode** runs `crop=W:H:X:Y,scale=outW:outH` — picks the largest target-ratio rectangle inside your input that doesn't require upscaling, then scales to the canonical output size. The position param controls X (for landscape→vertical) or Y (for vertical→landscape) so off-center subjects stay in shot. **Letterbox mode** runs `scale=outW:outH:force_original_aspect_ratio=decrease,pad=outW:outH:(ow-iw)/2:(oh-ih)/2:color=black` — fits the entire input inside the target frame and pads the empty axis with black bars. Loses no pixels but the video occupies less of the screen. **Blurred-background mode** runs a `split=2` filter that duplicates the input stream, scales one copy to fill the target by overflow-cropping, applies `boxblur=20:5` (radius 20, 5 passes — the signal-to-noise sweet spot for organic-looking blur), then overlays the original (fit-decreased to preserve all pixels) centered on top. Same look CapCut and InShot ship as their default for portrait-mode TikTok content. Output is always MP4 (H.264 CRF 23, AAC 128 kbps audio, +faststart). The convention output sizes (1080×1920 / 1080×1080 / 1080×1350 / 1920×1080) match what each platform actually downscales to during upload — shipping at the canonical size means uploads start there and don't get re-encoded by the platform's transcoder, which preserves quality.

Frequently asked questions

Is my video uploaded to a server?
No. NoCloud Media converts the aspect ratio entirely in your browser using WebAssembly. Your video file never leaves this tab — useful when you're repurposing client work, pre-release content, or anything personal.
Which fill mode should I pick?
**Blurred background** (default) is the user-pleasing one for landscape→vertical conversion — every TikTok / Reels you've seen with horizontal footage uses this. Pick it when you don't want to lose any pixels but also don't want black bars. **Crop** when the subject is in a known part of the frame (centered or shifted with the position slider) and you want the picture to fill the screen edge-to-edge. **Letterbox** for documentary / archive-style content where every pixel of the original matters and you don't want the picture transformed at all — the bars are the cost.
Why is the output 1080×1920 (or 1080×1350, etc.) — what if my source is smaller?
We always ship 1080 on the longer axis because that's what the social platforms expect. If your source is 720p or smaller, the output upscales to 1080. Modern platforms re-encode every upload anyway — landing at the canonical size means you control the quality of that upscale (with our libx264 settings) rather than letting TikTok / Instagram do it inside their transcoder, which is usually lower-quality.
Can the position slider keep an off-center subject in shot?
Yes — that's exactly what it's for. For landscape→vertical conversion (the most common case), the slider moves the crop window horizontally: -1 keeps the LEFT side of the source, 0 centers, +1 keeps the RIGHT side. For vertical→landscape, the slider moves vertically. The slider only appears in crop mode (letterbox + blurred-bg keep all pixels, so positioning is moot). Note that this is manual positioning — for ML-based subject detection (which is what CapCut Pro's 'Auto Reframe' does), you'd need a paid tool. Manual positioning covers 90% of cases.
Does this match CapCut Pro's 'Auto Reframe'?
Not exactly. Auto Reframe uses a machine-learning model to detect subjects and follow them across the clip. We use a manually-positioned crop window — no ML, no follow. For most content this is fine (most subjects are stable) and the outcome is identical. For content where the subject moves a lot across the frame (sports, dance, etc.) Auto Reframe is better — but you're paying for it. Our approach: drop, position, convert, done. If the subject moves a lot, pick blurred-background mode instead and avoid the cropping question entirely.
Why no 21:9 or 2.39:1 cinematic ratios?
Those don't have native upload support on TikTok / Instagram / YouTube — they get pillar-boxed by the platform either way. We focused on the four ratios that match real platform formats. If your downstream is a video player (not a social platform), letterbox mode lets you fit any source into any of these and you can post-process from there.
What's the maximum file size?
Same as our other tools: under 500 MB for smooth processing on most devices, 2 GB hard ceiling. Aspect ratio conversion always re-encodes the picture, so it scales with file size + clip length. Long videos (1 hour+) on a phone may hit memory limits.
Which browsers are supported?
Chrome, Edge, Firefox, and Safari 15+. We require WebAssembly and SharedArrayBuffer, both standard in modern browsers.

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