For precise 1GB, download a larger file then trim with ffmpeg:
: If you need high-quality visual content rather than just a dummy file, searching for "1GB" or "4K" on Pexels or Pixabay will provide royalty-free, high-resolution clips that often exceed several hundred megabytes or reach the 1GB mark depending on the resolution and duration chosen. Specialized Testing Resources download sample mp4 video files for testing 1gb new