YouTube Shorts and Instagram Reels use identical video specifications: 9:16 vertical aspect ratio, MP4 container, up to 1080p resolution, up to 3 minutes in length. A Short downloaded from YouTube is in the exact correct format to upload directly to Instagram Reels without any conversion, re-editing, or format adjustment.
YouTube Shorts are encoded at 9:16 vertical aspect ratio — identical to Instagram Reels. When you download a Short as an MP4, the video dimensions in the file are already 1080×1920 pixels (or equivalent vertical dimensions). Instagram's upload interface for Reels accepts vertical video files and displays them correctly without any cropping, letter-boxing, or scaling. You are not re-encoding or re-packaging the video — you are uploading the exact file that was served from YouTube's CDN, which already meets Instagram's technical requirements.
Cross-posting your own Shorts to Reels is straightforward and entirely within your rights as the creator. Cross-posting other creators' Shorts requires consideration of the original creator's rights — you should have explicit permission or the content should be clearly licensed for reuse. Many creators actively encourage cross-posting their content and some explicitly state so in their video descriptions. For content you did not create, always check the creator's permissions before reposting under your own account.
The same workflow works for TikTok videos to Instagram Reels. Download the TikTok video through dltkk.to without the watermark, save it to your Camera Roll, and upload to Instagram Reels. TikTok videos are also 9:16 vertical format and process identically. See the TikTok guide: Instagram Reels downloader.
Download Shorts at 1080p for the best quality upload. When Instagram reprocesses an uploaded video, it applies its own compression. Starting with the highest available quality (1080p) gives Instagram more to work with during its compression pass, resulting in a final Reel that looks better than one uploaded at 720p. Instagram's compression is applied regardless of what you upload — the quality of your source file determines the ceiling of the final result after compression.