API-governed Images Videos URL rules

Social Media Specifications

When you publish with Postly, your uploads go through platform APIs — not the mobile apps. That means formats, sizes, and aspect ratios must comply with the API specs to publish successfully.

API rules are the source of truth
A post that "works in the app" can still fail via API. Postly validates media to match what the platform API allows.
Use stable, public media URLs
Bulk publishing fails most often due to bad links. Use Postly Cloud or a public CDN for direct image/video file URLs.
Use recommended aspect ratios
Most platforms accept both portrait and landscape — but they each have "safe" recommendations that reduce rejections and ugly crops.
Guide

Media URL format rules (read this first)

These rules prevent most API upload failures — especially for Bulk Post (CSV / Google Sheets). Use direct/public links and avoid share-page URLs.

Image URL format rules
Examples that work
  • https://upload.wikimedia.org/wikipedia/commons/9/9a/Gull_portrait_ca_usa.jpg
  • https://cloud.postly.ai/media/your-image.jpg
  • https://static.cdn.example.com/banner-v3.png
Examples to avoid
  • https://www.instagram.com/p/XXXXXXXXX/
  • https://photos.google.com/share/XXXX
  • data:image/png;base64,iVBORw0K...
  • https://www.dropbox.com/s/FILE_ID/photo.png?dl=0
Use direct, public image file links (jpg/png/gif). Avoid links that require login, “share pages”, or base64 data URLs.
Video URL format rules
Examples that work
  • https://www.youtube.com/watch?v=dQw4w9WgXcQ
  • https://youtu.be/dQw4w9WgXcQ
  • https://vimeo.com/76979871
  • https://download.blender.org/peach/bigbuckbunny_movies/BigBuckBunny_320x180.mp4
  • https://cloud.postly.ai/media/your-video.mp4
Examples to avoid
  • https://youtube.com/shorts/XXXXXXXXXXX
  • https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=PL123456789
  • https://drive.google.com/file/d/FILE_ID/view?usp=share_link
  • https://www.dropbox.com/s/FILE_ID/video.mp4?dl=0
Use direct/public links or supported sources (YouTube watch / youtu.be, Vimeo, direct .mp4). Avoid Shorts URLs, playlist URLs, and private hosts like Drive/Dropbox share links.
Best practice: upload your media to Postly Cloud to get stable, public URLs that won’t break later.
Guide

Platform specs

Use the search to find a platform fast. Each section links to the official platform API docs.

Tip: search "9:16", "JPEG", "MP4", "carousel", "thumbnail", etc.

TikTokYouTubeInstagramFacebookThreadsX (Twitter)LinkedInPinterestGoogle Business ProfileTelegramRSSBluesky
Reminder
The platform APIs govern what can be published. Specs can change; the "API docs" link in each platform section is the authoritative source.

TikTok

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
TikTok API publishing is strict about container/encoding. Even when the native app accepts something, the API may reject unsupported encodes or incompatible dimensions.
API-safe recommendations
Vertical 9:16 (1080×1920)MP4 (H.264 + AAC)Avoid variable frame rates when possible

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Video (recommended)

API

• Recommended: 9:16 vertical

• Common export: 1080×1920

• Container: MP4 is the safest

• Audio: AAC is the safest

Text

API

• Captions are API-limited

• Keep hashtags reasonable (avoid spam filtering)

Images

Postly

• Image publishing not supported at the moment.

Important Notes
Using a share-page URL instead of a direct media file link
Important Notes
Odd aspect ratios (very wide panoramas) can fail in API flows
Important Notes
Non-standard codecs/encodes (API rejects even if the app plays it)

YouTube

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
YouTube uploads are governed by YouTube upload rules. If your upload exceeds platform limits or uses unsupported containers/codecs, the API upload will fail.
API-safe recommendations
16:9 (standard videos)9:16 (Shorts)MP4 (H.264 + AAC)1080p+ preferred

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Video

API

• Max upload: up to 12 hours (account-dependent)

• Max file size: up to 256 GB (account-dependent)

• Formats commonly accepted: MP4, MOV, AVI, WMV, MPEG-PS, FLV, 3GPP, WebM

Thumbnails

API

• Recommended: 1280×720

• Formats: JPG/PNG

• Keep file size small for reliability

Text

API

• Title + description are API-enforced

• Keep titles concise and avoid excessive hashtags

Important Notes
YouTube Shorts will publish automatically once the video meets the Shorts specifications: Vertical and below 60 seconds. This happens even if you choose a different category ID while publishing. If your video meets the Shorts criteria, it will be published as a Short regardless of the category you select.
Important Notes
Very long videos or huge files can fail if your channel/account has restrictions
Important Notes
Non-standard containers/codecs can upload but fail processing

Instagram

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Instagram’s API can be stricter than the Instagram app. Postly follows the API rules to publish reliably across accounts and business permissions.
API-safe recommendations
Square 1:1 (1080×1080)Portrait 4:5 (1080×1350)Vertical 9:16 (Stories/Reels)JPEG for imagesMP4 for video

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• API-safe max size: ~8MB

• Aspect ratios: 1:1, 4:5, 9:16 depending on placement

• Most reliable: JPEG

• Carousels: multiple images supported (API-enforced limits)

Video

API

• Most reliable: MP4 (H.264 + AAC)

• Reels/Stories: vertical 9:16 preferred

• Keep duration within the post type limits (API-enforced)

Text

API

• Captions are API-limited

• Hashtag stuffing can reduce reach (and may trigger moderation)

Important Notes
Using PNGs/GIFs where the API expects JPEG can fail
Important Notes
Incorrect aspect ratio for the chosen media type (Reels/Stories want vertical)
Important Notes
Oversized files / slow hosts can time out during ingestion

Facebook

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Facebook API publishing enforces media constraints (dimensions, encoding, size). Postly validates against these to reduce “published in app but fails in API” cases.
API-safe recommendations
Square 1:1Landscape 16:9Vertical 9:16 (Stories/Reels)JPEG/PNG for imagesMP4 for video

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• API-safe max size: ~4MB

• Feed supports 1:1 or 4:5 in feed

• Stories/Reels: 9:16

• Formats: JPEG/PNG are safest

Video

API

• Recommended: MP4

• Feed supports multiple aspect ratios

• Reels/Stories prefer 9:16

Text

API

• Text limits depend on endpoint and post type

• Keep CTAs clean to reduce link preview issues

Important Notes
Mixing images + videos in the same post type can fail (depending on endpoint)
Important Notes
Share-page links instead of direct file links

Threads

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Threads uses API rules similar to other Meta surfaces. Media + text limits are enforced by the API and can be stricter than the app experience.
API-safe recommendations
Square 1:1Portrait 4:5JPEG for imagesMP4 for videos

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Text

API

• Text is API-limited

• Replies and thread timing can be API-rate limited

Images

API

• Recommended: 1:1 or 4:5

• Formats: JPEG/PNG (endpoint-dependent)

Video

API

• Recommended: MP4

• Keep durations short for best reliability

Important Notes
Overlong text or unsupported media can fail via API even if the app behaves differently

X (Twitter)

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
X media is validated during upload. If the API rejects the media, your tweet cannot be created. Postly follows the API limits for reliability.
API-safe recommendations
Images: JPEG/PNGVideo: MP4 (H.264 + AAC)Use standard 16:9 or 1:1

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• Formats: JPEG/PNG/GIF

• API-safe max image size: ~5MB

• Recommended aspect: 16:9 (landscape) or 1:1 (square)

• Keep file sizes small for API reliability

Video

API

• Recommended: MP4 (H.264 + AAC)

• Keep durations short for best reliability

• Frame rates and bitrates outside standard ranges can fail processing

Text

API

• Character limits are API-enforced

• Threads are supported via API publishing flows

Important Notes
GIF/video size limits are strict via API
Important Notes
Unsupported encodes or odd dimensions commonly fail

LinkedIn

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
LinkedIn upload and post creation are governed by LinkedIn’s APIs. Ensure formats and sizes comply to prevent upload failures or processing errors.
API-safe recommendations
Images: JPEG/PNGVideo: MP4Landscape 1.91:1 or Square 1:1

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• Formats: JPEG/PNG (safest)

• API-safe max image size: ~5MB

• 1:1 or ~1.91:1

• Multi-image posts are endpoint-dependent

Video

API

• Recommended: MP4

• Prefer 1080p exports

• Keep durations reasonable to reduce processing delays

Text

API

• Post length limits are API-enforced

• Avoid excessive hashtags/links to improve delivery

Important Notes
Videos with unusual codecs can upload but fail transcoding
Important Notes
Oversized files may time out during upload

Pinterest

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Pinterest pins are very sensitive to aspect ratio. The API enforces rules that keep pins readable and consistent in feeds.
API-safe recommendations
Pins: 2:3 (1000×1500)Square 1:1 (alternative)Video: vertical 9:16 or 2:3JPEG/PNG for imagesMP4 for video

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• Recommended: 2:3 (1000×1500)

• Allowed: 1:1 (square)

• Formats: JPEG/PNG

Video

API

• Recommended: vertical formats for best performance

• Container: MP4 safest

• Keep duration aligned to pin type expectations

Text

API

• Title/description limits are API-enforced

• Keep descriptions readable (keyword stuffing hurts distribution)

Important Notes
Ultra-wide images may crop badly or be rejected
Important Notes
Non-direct URLs will fail ingestion

Google Business Profile

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Postly publishes to Google Business Profile via API and must follow what the API supports. Compared to social networks, GBP has limited media support in automated publishing.
API-safe recommendations
Images: JPEG/PNGSquare 1:1 preferredKeep file sizes small

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

APIPostly

• Formats: JPEG/PNG

• 1 image per post (Postly)

• Recommended: 1:1

• Prefer clear, non-text-heavy visuals

Video

Postly

• Not supported in Postly for Google Business Profile

Text

API

• Post text is API-limited

• Keep CTAs short and clear

Important Notes
Postly only supports image posts for Google Business Profile (no video publishing).
Important Notes
Only 1 image per GBP post is allowed in Postly.

Telegram

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Telegram bot publishing depends on bot permissions and channel settings. Media limits can vary by bot method and hosting approach.
API-safe recommendations
Images: JPEG/PNGVideo: MP4Keep file sizes small for reliable sends

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• Formats: JPEG/PNG

• Recommended: 1:1 or 4:5

• For albums: keep sizes consistent to avoid layout issues

Video

API

• Recommended: MP4

• Shorter clips send more reliably

• Use stable hosting if sending by URL

Text

API

• Captions are API-limited

• Links and markdown formatting vary by client

Important Notes
Bot permissions not set correctly
Important Notes
Large videos can fail depending on method and hosting

RSS

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
RSS is not a social network API, but feeds must be valid and media enclosures must be direct links. If the feed is malformed, imports/publishing will fail.
API-safe recommendations
Valid RSS/Atom feed URLDirect media enclosure linksJPEG/PNG for images, MP4 for videos

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Text

Feed

• Titles/descriptions depend on your feed

• HTML support depends on consumer

Media

Enclosure

• Images/videos should be direct file links

• Keep file hosting stable to avoid broken imports

Important Notes
Invalid XML
Important Notes
Enclosure points to a share page instead of a file

Bluesky

These limits are enforced by the platform API. Your post must comply to publish successfully.

ImagesVideoAPI constraintsRecommended
API docs
Why this matters
Bluesky is strict about media size. If the API rejects the blob, the post cannot be created. Keep images small and use predictable dimensions.
API-safe recommendations
Images: JPEG/PNG (small)1:1 or 4:5 for previewsAvoid huge high-res exports

These are the most reliable formats for API publishing across common post types. If your media falls outside these, some platforms may reject uploads (even if the native app allows it).

Images

API

• API-safe max image size: ~1MB

• Formats: JPEG/PNG

• Prefer 1:1 or 4:5 for predictable preview

Video

API

• Video support varies by service rules

• Keep clips short and file sizes small for reliability

Text

API

• Text limits are API-enforced

• Mentions and links must follow platform rules

Important Notes
Large media commonly fails
Important Notes
Upload quotas may apply
Need help? Visit docs.postly.ai or use Bulk Post via Google Sheets for validations and guided uploads.