Guides · 16 articles
FFmpeg and rendering
Working FFmpeg commands for the jobs video makers actually have, and how code-drawn animations become MP4 files.
How to Turn Images into a Video with FFmpeg
To make a video from numbered images, FFmpeg reads the files in order and shows each one for a set time.
3 min readHow to Add Audio to a Video with FFmpeg
To add a separate audio file to a video, tell FFmpeg which video and audio streams to use. A stream is one part of a media file, such as its video or audio;…
3 min readHow to Join Videos with FFmpeg (concat)
To join existing video clips in FFmpeg, use the concat demuxer if their streams match. Stream copy avoids re-encoding.
3 min readHow to Burn Subtitles into a Video with FFmpeg
When you have a video and a separate subtitle file, FFmpeg can permanently draw the subtitle text onto the picture.
3 min readFFmpeg CRF Explained: Choosing Quality for H.264 and H.265
When you compress video with FFmpeg, the CRF setting controls the encoder’s quality target. CRF stands for Constant Rate Factor.
4 min readHow to Normalize Audio Loudness with FFmpeg
When audio clips in a video, podcast, or recording have uneven volume, loudness normalization brings their perceived loudness closer to a target.
3 min readFFmpeg drawtext: Adding Text to a Video
When you need to place a title, label, or other text over an existing video, FFmpeg’s drawtext filter renders the text into each video frame.
3 min readHow to Mix Voice and Music with FFmpeg
When you combine spoken narration with background music, keep the music below the voice and set a defined length for the finished audio.
3 min readHow to Render an HTML Canvas Animation to MP4
To turn an animation drawn in an HTML <canvas> into an MP4, record the canvas as a video stream in the browser, then convert the recording.
4 min readRendering Video Frames with Headless Chrome and Puppeteer
When you create video scenes as web pages, Puppeteer uses Chrome to render each scene as an image. Headless Chrome runs without a visible window, and…
4 min readHow to Trim and Cut a Video with FFmpeg
To shorten an existing video or remove a section from its middle, use FFmpeg from the command line. Choose between copying the video streams, which is fast…
3 min readHow to Resize and Scale a Video with FFmpeg
Use FFmpeg from the command line when a video is too large, needs to fit a screen, or has the wrong shape for a platform.
4 min readHow to Extract Audio from a Video with FFmpeg
To save audio from a video, use FFmpeg, a command-line tool for reading and converting media. The -vn option omits the video, and -c:a copy copies the audio…
3 min readHow to Speed Up or Slow Down a Video with FFmpeg
When you change a video's playback speed, decide how to handle its audio. FFmpeg handles video timing with the setpts filter and audio tempo with the atempo…
3 min readHow to Turn a Video into a GIF with FFmpeg
To make an animated GIF from a video clip, use FFmpeg to choose frames, resize them, and encode them as an animation.
2 min readHTML Canvas Animation: How to Animate with JavaScript
To animate an HTML canvas, JavaScript clears the drawing area, moves an object, and draws it again in a loop.
4 min readVideos made with explainroo
A coding agent made each of these with explainroo, from the script to the finished MP4.
- YouTube 16:9
- Midnight look
How a cache makes a website faster
A cache keeps a copy of a page the server already built, so the next visitor gets it right away. When the data changes, that copy has to be replaced.
- YouTube 16:9
- Blueprint look
What an API does
An API is how one program asks another for something, shown with an online shop that asks a shipping service for a delivery date.
Free and open source
Make your own with your AI agent
explainroo lets a coding agent like Claude Code or Codex make narrated explainer videos and product demos. The voice, the word timing and the rendering run on your own computer, with no API key and no cost per video.
Copy this into your AI agent
Make me a short explainer video about [your topic]. Use explainroo for it: clone https://github.com/vincentsch/explainroo, read its AGENTS.md and follow the steps.
Made with explainroo: How a cache makes a website faster