flawless-webvidcap

Flawless, CPU-bound, video capture utility with no frame drops. Originally developed for streaming graphics.

Requirements

• ffmpeg program must be installed on server
  • https://command-not-found.com/ffmpeg
• puppeteer javascript library - https://pptr.dev/
  • install with npm

Usage

npm install puppeteer # install requirement into node_modules directory

./record-parallel (url) (width px) (height px) (RESERVED) (RESERVED) (output video format) (number of chunks)

• pass anything for "reserved" arguments - they are placeholders to make the chunk recording parameters match the subprocess parameters for less confusion.
  • TODO: fix this

Output Formats

• webm
• mp4
  • mp4 x264 codec does not support transparency
  • mp4 x264 requires even sizes of pixels for width and height of video
• mov
  • raw RGBA PNG frames in MOV container -> high memory usage, source quality video

Details

• this solution optimizes really well. by breaking it into pieces, the parts could even be completed on multiple servers!
  • works by updating the offsets of all videos / animations while running
• steps through frame by frame and stitches together a video at the end
  • sets offset of each video playing on the page to the current timestamp
• recording is actually possible on CPU-only servers!
  • this takes more time. approximately 1 minute to download a five-second 1080 video using 16 cores
• supports animated GIFs and animated PNGs (APNG)
  • breaks each animated GIF or APNG into multiple images which are replaced within the browser using data URLs
  • GIF and APNG extractor program is passed input from within javascript and retrieves the output images from filenames
• uses hooks to handle setInterval and clearInterval callbacks when needed for recording
• able to break into chunks and record in parallel for speed
  • the last few chunks are smaller than the rest in order to optimize workflow and CPU usage - practical fine tuning

Execution Steps

• export a PNG for each frame. use parallel processes to generate different "chunks" starting at offsets
• stitch them together using ffmpeg

Known Issues

• no support for different framerates of animated PNGs - assume 30 FPS