Book Trailer Specs: Ideal Length and Aspect Ratio by Platform
If you’re making a book trailer, the single most important technical decision you’ll make is which aspect ratio to shoot or export in — and that answer depends entirely on where the video will live. YouTube, Instagram Reels, and TikTok each have different native formats, different audience expectations, and different algorithmic preferences for video length. Getting these specs right means your trailer fills the screen the way it was designed to, rather than appearing with awkward black bars or getting cropped at the edges.
Why Aspect Ratio Matters More Than Resolution
Resolution is the number of pixels in your video — 1920×1080, for example. Aspect ratio is the shape: the proportional relationship between width and height. On video platforms, aspect ratio is the more consequential of the two, because a video shot in the wrong ratio for a platform will be pillarboxed (black bars on the sides) or letterboxed (black bars top and bottom), both of which reduce visual impact and, on some platforms, trigger the algorithm to show your content to fewer people.
YouTube is a landscape-first platform built around the 16:9 widescreen format — the same proportions as a modern television. Instagram Reels and TikTok are both mobile-first, vertical platforms that use 9:16, which fills a phone screen held upright. These two formats are fundamentally incompatible: a 16:9 video posted to TikTok will have large black bars and feel out of place, while a 9:16 vertical video on YouTube will appear as a narrow strip with grey sidebars.
YouTube: 16:9 at 1920×1080, 30–90 Seconds
YouTube’s recommended aspect ratio is 16:9 at a minimum resolution of 1920×1080 pixels (1080p HD). The platform supports resolutions up to 4K, but 1080p is the practical standard for book trailers. YouTube does not impose a strict maximum length for standard uploads, but engagement data consistently points to 30–90 seconds as the effective window for promotional content. Viewers will tolerate up to two minutes if the content earns their attention, but drop-off increases sharply beyond that point.
YouTube also supports the 9:16 vertical format for Shorts — videos of 60 seconds or less — which appear in a dedicated feed separate from standard search results. If you want your trailer to appear in standard YouTube search and on channel pages, stick with 16:9.
Instagram Reels: 9:16 at 1080×1920, Up to 3 Minutes
Instagram Reels use a 9:16 vertical format at 1080×1920 pixels, with a minimum frame rate of 30 FPS. In early 2025, Instagram extended the maximum Reel length from 90 seconds to 3 minutes (180 seconds), and Reels up to 3 minutes are now eligible for algorithmic recommendation in the main Reels feed. This is a meaningful change for authors who want to include a longer excerpt reading or a more cinematic opening.
That said, shorter Reels still tend to outperform longer ones in terms of completion rate, which is a key signal Instagram’s algorithm uses to decide how widely to distribute a video. A tight 45–60 second trailer will generally reach more new viewers than a two-minute one, even though the longer format is now technically permitted.
Instagram also displays a 1:1 square thumbnail on profile grids, so it’s worth considering how your vertical video crops to a square when choosing your opening frame.
TikTok: 9:16 at 1080×1920, with a 9–60 Second Sweet Spot
TikTok shares Instagram’s 9:16 vertical format at 1080×1920 pixels, with a minimum of 30 FPS. Technically, TikTok now allows uploads up to 60 minutes long — but that upper limit is almost meaningless for book trailers. Engagement data from TikTok Studio shows that 9–15 seconds is the optimal length for maximum organic reach, with 5–60 seconds being the practical recommended range. Videos beyond 60 seconds see a significant drop in completion rate, which is the primary metric driving TikTok’s distribution algorithm.
TikTok accepts MP4 files up to 30GB and also supports 1:1 square and 16:9 landscape formats, though neither performs as well as native 9:16 vertical in the For You feed. If you have a 90-second trailer cut, trimming a 15–30 second teaser specifically for TikTok is worth the extra export step.
The Two-Version Approach
The most efficient way to handle multi-platform distribution is to produce two master exports from the same footage: a 16:9 landscape cut (60–90 seconds) for YouTube, and a 9:16 vertical cut (30–60 seconds) for Instagram Reels and TikTok. This avoids the quality loss and awkward framing that comes from automatically converting between aspect ratios.
When shooting or editing, keep your most important visual elements — a book cover, a key image, any text on screen — centred in the frame and away from the edges. A safe zone of roughly 10–15% inward from each edge will survive cropping to either format without losing critical content.
Summary: Platform Specs at a Glance
YouTube requires 16:9 at 1920×1080 and rewards trailers in the 30–90 second range. Instagram Reels and TikTok both use 9:16 at 1080×1920; Instagram allows up to 3 minutes but favours shorter content, while TikTok’s algorithm strongly favours 9–60 seconds. Shooting to the correct aspect ratio for each platform — or planning a two-version export from the start — will give your book trailer the best chance of filling the screen and the algorithm’s attention.
