A waveform image is the thing every podcast page, audio embed, and video caption card needs and no export dialog produces. This draws one at the size you are going to use it.
Bars, filled, or line
Bars are the familiar player look: discrete rectangles with a gap between them. Bar width and gap are both in output pixels, so the density you set is the density you get.
Filled draws a solid shape between the upper and lower envelope, which reads better at small sizes and in print. Line draws only the outline, which suits a light background and a thin stroke.
Mirroring puts the envelope above and below a centre line. Turning it off draws only the positive half, anchored to the bottom, which is the shape most video captions use.
PNG or SVG
Both come from the same geometry. The PNG is rasterised at the exact width and height set on the canvas controls; the SVG carries the same bars as vector shapes and scales to any size afterward.
Pick SVG when the drawing goes into a design tool or a page that might render it at a different width. Pick PNG when it goes into a video timeline or a CMS that does not accept SVG.
Peaks JSON
The envelope is exported as interleaved minimum and maximum pairs, normalised to -1 through +1, with the sample rate and samples-per-pixel alongside. That is the format wavesurfer.js and peaks.js read.
Serving that file next to the audio means a player draws its waveform on first paint instead of after downloading and decoding the whole track. On a one hour podcast episode that is the difference between an instant render and several seconds of blank space.
The envelope
Peaks are read progressively while the file streams, so the drawing appears before the whole file has been scanned and sharpens as it finishes. Each bar takes the lowest and highest sample in the slice it covers, which is what keeps a single transient visible instead of averaging it into the surrounding level.
Sizing
Very wide canvases with narrow bars produce a lot of shapes. A 4000px image with 1px bars and no gap is 4000 rectangles in the SVG, which most editors handle but some older ones do not. Widen the bars or add a gap if the file needs to stay small.