Your book trailer thumbnail is the still image people see before they press play. On YouTube and a Facebook Page you can upload your own and change it later. Instagram Reels and LinkedIn lock the image once you post, so the choice is final. On TikTok you pick a frame from the video.
How Does Each Platform Handle a Book Trailer Thumbnail?
Platforms handle the still image on a video in two different ways, and some offer both. Some let you drag along the video’s timeline after upload and pick a frame out of it. Others let you upload a separate picture you have prepared.
On YouTube, uploading a video and setting its thumbnail are not on the same footing. Uploading needs no verification at all, but a custom thumbnail does: YouTube classes thumbnails as an intermediate feature, unlocked by verifying your channel with a phone number. If the upload button seems to be missing, that is usually why, and you can check under Settings, then Channel, then Feature eligibility. On LinkedIn, the desktop share box carries a Video thumbnail control with an upload button, so set the image there as you post.
Which Platforms Let You Change the Thumbnail Later?
Instagram Reels and LinkedIn both fix a video’s thumbnail at the moment you post it, and neither lets you change it afterwards. Instagram’s Reels size and aspect ratio page says so plainly: “Right now, you can’t edit your cover photo after you’ve uploaded it.” LinkedIn goes further, because its restriction covers the whole post. Only the text can be edited, and shared rich media “such as photos, articles, documents, and videos – can’t be replaced”. On either platform, changing the image means deleting the post and putting it up again, which loses the views, comments and shares it has already gathered.
YouTube and Facebook Pages both let you go back and think again. In YouTube Studio you open Content, click the video, set a new thumbnail and save. On a Facebook Page you open Options, then Edit post, then Video options, where Change thumbnail offers a suggested image, one you upload, or a frame from the video. TikTok is the gap here. Its support page on editing and posting says you can select a cover “before posting a new video”, and describes no way to change one afterwards.
Platform by platform, both halves together:
| Where you post it | What you can set | Change it after posting? |
|---|---|---|
| YouTube video (not Shorts) | Upload an image in YouTube Studio | Yes |
| YouTube Shorts | Upload an image in Studio on a computer, or pick a frame in the app | Yes |
| Instagram Reels | Upload an image or pick a frame, before you share | No |
| TikTok, ordinary video post | Pick a frame at the Select cover step | TikTok’s help pages don’t say |
| Facebook Page video, on a computer | An automatic suggestion, an image you upload, or a frame | Yes |
| LinkedIn video, on desktop | Upload an image | No; delete and repost |
What Size Should a Book Trailer Thumbnail Be?
A book trailer involves two sets of pixel dimensions, and they are not the same. The sizes below describe the still image only. The video itself has its own resolution and export settings, and the two do not have to match.
YouTube’s guidance on thumbnail size has moved, and size guides still in circulation print the older figure. It now recommends 3840 × 2160 pixels for a video thumbnail and 2160 × 3840 for a Short, with a minimum width of 640 pixels for videos and a minimum height of 640 pixels for Shorts. JPG and PNG are both accepted.
YouTube’s file size limit for a thumbnail depends on the device you upload from, which is why sources contradict each other. From a phone the ceiling is 2 MB. From a computer it is 50 MB. Design at the full 3840-pixel size for your orientation, upload from a computer, and neither limit will trouble you.
Instagram publishes one figure: a recommended Reels cover image of 420 × 654 pixels, a ratio of about 1:1.55. Past that its help pages are quiet, and we could find no stated file type, file size limit or minimum dimension for a Reels cover, nor anything describing how the cover is cropped on your profile grid. Nor could we locate any cover dimensions published by TikTok. Where a platform does not publish a number, the practical default is to match the shape of the video: 16:9 for a landscape trailer, 9:16 for a vertical one.
The practical rule is short. Decide the image before you post to Instagram Reels, LinkedIn or TikTok, because none of the three is documented as letting you change your mind afterwards. On YouTube and a Facebook Page you can post first and refine later. Which platforms to put the trailer on in the first place is a separate question, and one we covered in where to share your book trailer.
Frequently Asked Questions
Is a YouTube thumbnail still 1280 × 720?
Not as a recommendation. YouTube’s current guidance asks for 3840 × 2160 pixels for a video thumbnail, with a minimum width of 640 pixels. A 1280 × 720 image clears that stated minimum and still uploads, so nothing breaks, but it is no longer the size YouTube asks for.
Can I change a TikTok cover after I post?
TikTok’s own support page says you can select a video cover “before posting a new video”, and it describes no way to change one afterwards. We could find nothing elsewhere in TikTok’s support pages either. Choose it carefully at the Select cover step, because you may not get a second chance.
Should my book trailer thumbnail just be my book cover?
It can be, and for a trailer it is the obvious choice. No platform publishes a rule about what a trailer thumbnail should show, so this is a judgement rather than a requirement. The one practical constraint is shape: a book cover is a tall rectangle and a YouTube thumbnail for a long-form video is a wide one, so a cover dropped into a 16:9 frame leaves empty space on either side of it.
Do thumbnails actually get a book trailer more views?
Nobody has published a figure worth quoting. In its own thumbnail and title tips, YouTube states that 90% of its best-performing videos have custom thumbnails, but it does not define “best-performing”, name a sample or publish a method, and the sentence describes which videos have custom thumbnails rather than what adding one does. The widely repeated claim that faces raise click-through rates by around 30% traces back to no original study we could find.
How is this different from my book cover at thumbnail size?
They are two separate images doing two separate jobs. A book trailer thumbnail fronts a video, and its shape follows the video: wide for a landscape trailer, tall for a vertical one. Your book cover is a tall image shown small on a retailer’s storefront beside dozens of competing books, and it has its own dimensions and file specifications for each platform.
