Vertical Video Looks Wrong? Aspect Ratio Fixes

Picture this: you're a fitness coach streaming a workout to TikTok and YouTube at the same time. On TikTok it looks perfect — full screen, vertical, great. Then you check the YouTube replay and your head is cut off, the sides are black bars, and the whole thing looks like it was filmed through a mailbox slot.

That's an aspect ratio mismatch. It happens when the shape of your video doesn't match the shape the platform expects. Here's how to fix it.

The 10-second version

• TikTok and Instagram want vertical video: 9:16 (1080 × 1920)
• YouTube and Twitch want horizontal video: 16:9 (1920 × 1080)
• If you stream one shape to a platform expecting the other, you get black bars, cropping, or stretching
• Pick the shape that matches your most important platform, and set it before you go live

Why it looks wrong

Most creators run into this when they multistream to a mix of vertical-first platforms (TikTok, Instagram) and horizontal-first platforms (YouTube, Twitch) in the same session.

Your camera captures one rectangle. Every destination receives that same rectangle. TikTok displays it as a tall phone screen; YouTube displays it as a wide TV screen. If you shot vertical and YouTube shows it wide, you get black bars on the sides (letterboxing). If you shot horizontal and TikTok shows it tall, TikTok crops the sides off — which is how heads get cut off.

Neither platform is broken. They're just showing your video in the only shape they know.

Fix it in the Castream app

The easiest fix is to decide your orientation before you tap Go Live:

1. Open the Castream app and frame your shot
2. Hold your phone vertical if TikTok or Instagram is your main audience
3. Hold your phone horizontal (landscape) if YouTube or Twitch matters more
4. Check the preview — what you see is what every destination gets

Don't rotate mid-stream. Switching orientation halfway through confuses the encoder and every platform will show a glitchy, sideways mess for a few seconds.

Fix it in OBS

If you're streaming through OBS into Castream, set your canvas to match your priority platform:

• Vertical-first (TikTok/Instagram): Settings → Video → Base Resolution 1080 × 1920, Output Resolution 1080 × 1920
• Horizontal-first (YouTube/Twitch): Base and Output at 1920 × 1080

Keep both resolutions identical unless you have a reason not to — mismatched base and output resolutions cause soft, blurry video.

For the full OBS walkthrough, see How to Stream to YouTube, Twitch & More Using OBS and Castream.

The common symptoms, decoded

Black bars on the sides (YouTube/Twitch): You streamed vertical to a horizontal platform. Either accept the bars (totally normal — Shorts-style content does this all the time) or stream horizontal instead.

Sides cut off (TikTok/Instagram): You streamed horizontal to a vertical platform. TikTok zooms in to fill the screen. Fix: stream vertical, or keep important action in the center third of a horizontal frame.

Everything looks stretched: Your output resolution doesn't match your canvas. In OBS, make Base and Output resolutions the same aspect ratio. In the app, just restart the stream in the correct orientation.

Looks fine live, wrong in the replay: Some platforms re-encode replays differently than live. If the live looked right, your settings are fine — it's the platform's replay processing, not your stream.

One more thing

If TikTok is in your destination mix, vertical 1080 × 1920 at 30fps is the sweet spot — it's what TikTok's player is built for. Our TikTok RTMP guide and Instagram RTMP guide both cover the recommended settings per platform, and the mobile setup guide has framing tips for phone streaming.

Pick one shape, commit to it before you go live, and stop checking the replay in horror. You've got this.