> ## Documentation Index > Fetch the complete documentation index at: https://typecast.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. # Create shorts with AI Turn one video or image into a captioned vertical short with Typecast narration. Give the skill instructions to your AI agent, then review the script and preview. ## What you need A Typecast API account is all you need to get started. ## 1. Give the skill to your agent Open the section below, copy the complete skill text, and send it to your AI coding agent. The text is self-contained and does not require access to a separate repository. ````markdown --- name: create-typecast-shorts description: Create a captioned 9:16 short or reel from one rights-cleared local video or image using Typecast narration, timestamp output, and ffmpeg. Use when a user asks to make a short-form video, reel, vertical video, narrated social clip, or Typecast-powered short from media they own or are authorized to use. --- # Create Typecast Shorts Create one 1080×1920 MP4 from a local video or image, Typecast narration, and timestamp-aligned subtitles. ## Boundaries - Accept only an attached file or local file the user owns or is authorized to use. - If rights are unclear, ask the user to confirm them before processing. - Do not search for, download, scrape, or reuse third-party video, news, or social media. - Do not remove logos, watermarks, attribution, or embedded subtitles to conceal a source. - Do not upload or publish the result. Return local artifacts for user review. - Do not print, log, or place a Typecast API key in chat, commands, scripts, or output files. - Support one background video or image per run. Ask the user to choose one when several are provided. ## Workflow ### 1. Confirm inputs Collect: - Local media path - Topic or finished script - Language - Target duration; default to 45–60 seconds - Typecast voice ID, or permission to open the interactive voice picker - Output directory inside the current workspace Use these defaults unless the user specifies otherwise: - 1080×1920, 30 fps - Center crop to fill the frame - Discard source audio - White bottom-centered subtitles with a black outline Confirm media rights, the final script, and the voice before making the paid TTS request. ### 2. Check the environment Run: ```bash command -v cast command -v ffmpeg command -v ffprobe cast --help ffmpeg -filters 2>/dev/null | grep subtitles ``` If a command or the ffmpeg `subtitles` filter is missing, explain the missing dependency. Install it only with user approval. After installing cast with Go, add it to the current shell without hardcoding the user's home directory: ```bash export PATH="$(go env GOPATH)/bin:$PATH" ``` For cast installation, use the official options: ```bash brew install neosapience/tap/cast # or go install github.com/neosapience/cast@latest ``` Authenticate with `cast login` so the key is entered in its own prompt. Never ask the user to paste the key into chat. ### 3. Create a clean work directory Create a new, explicit directory inside the current workspace. Do not overwrite an existing output. Keep these artifacts: ```text script.txt script-tts.txt narration.wav captions.srt preview.mp4 final.mp4 ``` Work from this directory while rendering so `captions.srt` does not require platform-specific path escaping. ### 4. Prepare the script If the user supplied only a topic, draft a concise script with: 1. Hook 2. Main point 3. Supporting detail 4. Closing line Save the approved text as `script.txt`. Create `script-tts.txt` separately. Change only pronunciations that TTS may misread, such as numbers, abbreviations, URLs, symbols, or mixed-language terms. Preserve the meaning and never overwrite `script.txt`. ### 5. Select a voice and generate audio plus captions If no voice ID was provided, run: ```bash cast voices pick ``` After approval, generate narration and SRT together: ```bash cast "$(cat script-tts.txt)" \ --voice-id VOICE_ID \ --language LANGUAGE_CODE \ --format wav \ --out narration.wav \ --timestamp-out captions.srt \ --timestamp-format srt ``` Use ISO 639-3 language codes such as `kor`, `eng`, or `jpn`. For Japanese or Chinese, cast automatically selects character-level alignment; use the latest cast release if that behavior is unavailable. Do not fall back to Whisper merely to create timestamps. Typecast captions already returns aligned audio and subtitles without another model or dependency. ### 6. Inspect the source Run: ```bash ffprobe -v error -show_entries stream=codec_type,width,height,duration \ -of default=noprint_wrappers=1 "SOURCE_PATH" ``` Use the video command for a video source and the image command for a still image. Quote every user-provided path. ### 7. Render a 15-second preview For a video: ```bash ffmpeg -y -stream_loop -1 -i "SOURCE_PATH" -i narration.wav \ -filter_complex "[0:v]scale=1080:1920:force_original_aspect_ratio=increase,crop=1080:1920,setsar=1,subtitles=captions.srt:force_style='FontSize=16,PrimaryColour=&H00FFFFFF,OutlineColour=&H00000000,BorderStyle=1,Outline=1.5,Shadow=0,Alignment=2,MarginV=80'[v]" \ -map "[v]" -map 1:a -t 15 -shortest -r 30 \ -c:v libx264 -preset medium -crf 20 \ -c:a aac -b:a 192k -movflags +faststart preview.mp4 ``` For an image: ```bash ffmpeg -y -loop 1 -framerate 30 -i "SOURCE_PATH" -i narration.wav \ -filter_complex "[0:v]scale=1080:1920:force_original_aspect_ratio=increase,crop=1080:1920,setsar=1,subtitles=captions.srt:force_style='FontSize=16,PrimaryColour=&H00FFFFFF,OutlineColour=&H00000000,BorderStyle=1,Outline=1.5,Shadow=0,Alignment=2,MarginV=80'[v]" \ -map "[v]" -map 1:a -t 15 -shortest -r 30 \ -c:v libx264 -preset medium -crf 20 \ -c:a aac -b:a 192k -movflags +faststart preview.mp4 ``` Show the preview to the user. Check framing, subtitle readability, pronunciation, and timing before the full render. If center crop cuts off important content, replace the scale and crop portion with: ```text scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black ``` ### 8. Render and verify the final video After preview approval, rerun the matching command without `-t 15`, add `-shortest`, and write `final.mp4`. Verify: ```bash ffprobe -v error \ -show_entries stream=codec_name,width,height -show_entries format=duration,size \ -of default=noprint_wrappers=1 final.mp4 ``` Require: - 1080×1920 video - H.264 video and AAC audio - Non-zero duration and size - Narration and subtitles ending with the video Return the output directory and artifact list. Remind the user to review the complete video before publishing it themselves. ## Failure handling - For 401 or 403 from cast, re-run `cast login` and verify the Global API plan without exposing the key. - For 402 or 429, report the billing or rate-limit response; do not retry repeatedly. - If timestamp flags are unavailable, update cast instead of adding a parallel transcription stack. - If ffmpeg cannot load subtitles, use an ffmpeg build with libass. - If rendering fails, preserve all existing artifacts and rerun only the failed step. ```` ## 2. Create it through conversation Describe the short you want, then change any of these details as you talk with your agent. | What you can change | Try saying | | -------------------- | ---------------------------------------------------------------------------- | | Script and message | “Open with a stronger hook” or “focus on one key idea.” | | Voice and tone | “Try a brighter, more energetic voice” or “read it more calmly.” | | Length and pacing | “Keep it under 30 seconds” or “make the pacing a little faster.” | | Captions and visuals | “Split the captions into shorter lines” or “keep the main subject in frame.” | Keep talking with your agent and refine each part until the short feels right. ## 3. Review and approve The agent asks you to approve: 1. The script and Typecast voice 2. A 15-second preview with narration and captions 3. The final render After approval, you receive a 1080×1920 MP4 along with the script, narration, and SRT caption files. When uploading media, clearly identify its copyright source. ## What the agent handles Checks and installs the cast CLI and ffmpeg after asking for approval. Prepares the script and generates Typecast narration securely. Creates timestamp-aligned SRT captions from the same narration. Renders a preview and final 9:16 MP4 for your review. You only need to provide the media, topic, and approvals. Let the agent handle the command-line tools and rendering steps.