The WhatsApp channel runs on Baileys Web. This page covers media handling rules for send, gateway, and agent replies.

For inline audio and video in the Control UI and native apps, including portable formats, byte limits, and lazy transcoding, see Media playback.

Goals

• Send media with an optional caption via apus message send --media.
• Allow auto-replies from the web inbox to include media alongside text.
• Keep per-type limits sane and predictable.

CLI Surface

apus message send --target <dest> --media <path-or-url> [--message <caption>]

• --media <path-or-url> — attach media (image/audio/video/document); accepts local paths or URLs. Optional; caption can be empty for media-only sends.
• --gif-playback — treat video media as GIF playback (WhatsApp only).
• --force-document — preserve original image bytes on Slack, or send images, GIFs, and videos as documents on Telegram and WhatsApp, to avoid channel compression.
• --reply-to <id>, --thread-id <id>, --pin, --silent — delivery/threading options shared with text-only sends.
• --dry-run — print the resolved payload and skip sending.
• --json — print the result as JSON: { action, channel, dryRun, handledBy, messageId?, payload } (payload carries the channel-specific send result, including any media reference).

Message tool attachment metadata

For buffer attachments, contentType takes precedence over mimeType; a data URL's MIME type is used only when neither is supplied. For reply, sendAttachment, upload-file, and setGroupIcon, top-level MIME metadata also takes precedence over the selected attachments[] entry. Hydration carries that choice as contentType and uses it to infer a missing filename. Explicit filenames are preserved. This metadata precedence does not change MIME detection when media bytes are loaded or staged.

WhatsApp Web channel behavior

• Input: local file path or HTTP(S) URL.
• Flow: load into a buffer, detect media kind, then build the outbound payload per kind:
  • Images: optimized to fit under channels.whatsapp.mediaMaxMb (default 50MB). Opaque images are recompressed to JPEG (default side ladder starts at 2048px, descending on repeated size misses); images with transparency are kept as PNG. If the source is already an acceptable JPEG/PNG/WebP within the size and side-length budget, the original bytes are preserved unchanged instead of being recompressed, even when a stale .heic or .heif filename remains after conversion. GIFs and animated WebP images retain their original bytes; images exceeding byte caps or explicit model dimension limits are rejected rather than flattened to one frame.
  • Audio/voice: unless already native voice audio (.ogg/.opus, or audio/ogg/audio/opus), outbound audio is transcoded via ffmpeg to Opus/OGG (48kHz mono, 64kbps, capped at 20 minutes) before sending as a voice note (ptt: true).
  • Video: pass-through up to 16MB.
  • Documents: anything else, up to 100MB, with filename preserved when available.
• WhatsApp GIF-style playback: send an MP4 with gifPlayback: true (CLI: --gif-playback) so mobile clients loop it inline.
• MIME detection prefers sniffed magic bytes, then the file extension, then response headers; a generic sniffed container (application/octet-stream, zip) never overrides a more specific extension mapping (for example XLSX vs ZIP).
• Caption comes from --message or reply.text; empty caption is allowed.
• Logging: non-verbose shows ↩️/✅; verbose includes size and source path/URL.

Auto-Reply Pipeline

• getReplyFromConfig returns a reply payload (or array of payloads) with text?, mediaUrl?, and mediaUrls? among other fields.
• When media is present, the web sender resolves local paths or URLs using the same pipeline as apus message send.
• Multiple media entries are sent sequentially if provided.

Generated attachments stay separate from later tool-error warnings. Image references in errors or reasoning do not select or discard generated attachments.

When a channel converts Markdown image links into attachments, image syntax inside code blocks or inline code, and escaped image syntax, stays in the text. Inline image destinations retain their URL punctuation.

Inbound Media To Commands

• When inbound web messages include media, Apus downloads it to a temp file and exposes templating variables:
  • {{AttachmentUrl}} — original URL or provider reference for the current attachment.
  • {{AttachmentPath}} — local temp path written before running the command.
  • {{AttachmentContentType}} — MIME content type.
  • {{AttachmentDir}} — directory containing the local path.
  • {{AttachmentIndex}} — zero-based source fact index.
• When a per-session Docker sandbox is enabled, inbound media is copied into the sandbox workspace and the attachment path/reference is rewritten to a sandbox-relative path like media/inbound/<filename>.
• {{MediaPath}}, {{MediaUrl}}, {{MediaType}}, and {{MediaDir}} remain deprecated compatibility aliases for the {{Attachment*}} names that replaced them in 2026.8.1. Their approved removeAfter date is 2026-10-01, gated on a clean published-plugin artifact sweep; migrate before then. See Media legacy projection.
• Media understanding (configured via tools.media.* or shared tools.media.models) runs before templating and can insert [Image], [Audio], and [Video] blocks into Body.
  • Audio sets {{Transcript}} and uses the transcript for command parsing so slash commands still work.
  • Video and image descriptions preserve any caption text for command parsing.
  • Native-vision models can skip the [Image] summary block. See Rules and behavior for the rule and its MiniMax exception.
• By default only the first matching image/audio/video attachment is processed; use tools.media.<capability>.attachments to select multiple attachments.

Limits and errors

Outbound send caps (WhatsApp web send)

• Images: up to channels.whatsapp.mediaMaxMb (default 50MB) after optimization.
• Audio/video: 16MB cap (shared default; overridden by mediaMaxMb when sending through WhatsApp).
• Documents: 100MB cap (shared default; overridden by mediaMaxMb when sending through WhatsApp).
• Oversize or unreadable media produces a clear error in logs, and the reply is skipped. Size errors use readable byte units rather than rounding fractional caps to a whole MB.

Media understanding caps (transcription/description)

• Image default: 10MB (override with tools.media.image.maxBytes, or per tools.media.models[] entry with maxBytes).
• Audio default: 20MB (override with tools.media.audio.maxBytes, or per entry).
• Video default: 50MB (override with tools.media.video.maxBytes, or per entry).
• Oversize media skips understanding, but the reply still goes through with the original body.

Image description checks the source byte cap before resizing. Recognized images are then prepared for the selected model's declared image limits; each fallback starts from the same normalized original. Models without declared image limits keep those normalized bytes. agents.defaults.imageQuality remains an image-tool setting and does not change media-understanding preparation.

Notes for Tests

• Cover send and reply flows for image/audio/document cases.
• Validate size bounds after image optimization and the voice-note flag for audio.
• Ensure multi-media replies fan out as sequential sends.

Related

• Camera capture
• Media understanding
• Media playback
• Audio and voice notes