# Video checker https://flaghand.com/video-checker says whether a video will post on X, LinkedIn and TikTok, and what to change if it won't: length, file size, picture size, frame rate, video codec and sound, read from the MP4 or MOV's own headers. Free, no sign-up. The video never leaves your browser. ## How to use it 1. Drop or choose a video. 2. Read each network's verdict and what to change. 3. Copy the one ffmpeg line that fixes what a command can. An agent that read a file with ffprobe can hand its person the verdict as facts in the link's hash: https://flaghand.com/video-checker#length=48.2&size=43620000&width=1080&height=1920&fps=30&video=hevc&audio=aac&channels=2&file=mov. Full specs: https://flaghand.com/docs/guides/video-specs-tiktok-x-linkedin. ## Limits. ### X (Twitter) Length **2:20** Every account. Some can post longer. Frame rate **60 fps** Or less. Between 1:3 and 3:1, in 4:2:0 colour. Size **512 MB** MP4 or MOV, with AAC-LC sound in mono or stereo. ### LinkedIn Length **30:00** At least 3 seconds. Size **500 MB** At least 75 KB. File **MP4** Only MP4: convert a MOV first. ### TikTok Length **10:00** 3:00 on every account; 5 or 10 minutes on some. Frame rate **23–60 fps** H.264, HEVC, VP8 or VP9. Picture **360–4096** Pixels on each side. 1080 × 1920 fills the screen. ## Questions. ### What are Twitter’s (X’s) video requirements? An MP4 or MOV up to 2 minutes 20 seconds long, which every account can post; X lets some accounts post longer. Up to 512 MB and 60 fps, between 1:3 and 3:1, in 4:2:0 colour with AAC-LC sound in mono or stereo. H.264 is what X asks for. ### What are LinkedIn’s video specs? An MP4 from 3 seconds to 30 minutes long and from 75 KB to 500 MB. LinkedIn’s API takes MP4 only, so a MOV, like the ones an iPhone saves, needs converting first. ### What size should a TikTok video be? 1080 × 1920, a 9:16 video, fills a phone’s screen. TikTok takes 360 to 4096 pixels on each side and 23 to 60 fps, in H.264, HEVC, VP8 or VP9. Every account can post 3 minutes, and some 5 or 10. ### Why won’t my iPhone video post on LinkedIn? An iPhone saves a MOV file, and LinkedIn’s API takes MP4 only. Convert it to MP4 with the ffmpeg line the checker gives you, or export it as an MP4 from your editor. ### Is my video uploaded? No. The checker reads the file’s own headers in your browser, never its pictures or sound. Your video isn’t sent anywhere or stored, and the page sets no cookies. ### Where do these rules come from? LinkedIn’s are the checks Flaghand makes before you approve a post, from LinkedIn’s Videos API. TikTok’s come from its Content Posting API, and X’s from its API documentation and what its API takes: the documentation says 20 minutes, but the API refuses videos over 2:20 from most accounts. For every number, app and API side by side, read the [video specs guide](https://flaghand.com/docs/guides/video-specs-tiktok-x-linkedin). ## Flaghand The rules here are the checks Flaghand makes before an owner approves a post, so a video that passes here passes there. Flaghand is X and LinkedIn posting for AI agents: your agent drafts through Flaghand's API, CLI or MCP server, you approve the exact preview with your passkey, and Flaghand posts exactly that. Sign up at https://app.flaghand.com/start. In a chat app, add the connector at https://app.flaghand.com/mcp: its sign-in page creates the account. An agent with a shell can start the sign-up for its person over HTTP (https://flaghand.com/llms.txt, Quickstart). For agents: https://flaghand.com/llms.txt (this site) and https://app.flaghand.com/llms.txt (the product's agent guide).