Before converting a batch to WebP or AVIF in a browser, verify that the chosen encoder can produce that format. Display support is a separate capability from export support. A tool may use native Canvas encoding or a dedicated encoder, and those paths can support different formats on the same device.
Know which encoder is doing the work
A native browser Canvas export is not a universal AVIF encoder. MDN documents PNG as the required Canvas output and a fallback when another requested format is unsupported. Support for additional output types varies. A dedicated encoder can provide different capabilities, but the app must actually include and use it.
Test one file before the batch
Select a representative JPEG or PNG and keep the original. Choose the target format and export one candidate. Check the output with a file inspection tool or an application that reports the actual image type. The extension by itself is not evidence: a PNG with an .avif name remains a PNG.
If the actual format differs from the requested format, choose a supported output or use an encoder explicitly supporting the desired one. Lowering quality or renaming the file cannot add a missing encoder.
Compare appearance independently of the format choice
Use the same dimensions for competing candidates. Inspect gradients, fine texture, text and transparent edges, then adjust quality based on what the audience must see. Do not promise a fixed percentage saving or assume an AVIF export is always smaller than an already efficient WebP.
Check downstream acceptance
Open the candidate in the intended editor, website or upload form. An image format supported for browser viewing may still be rejected by an upload service. Keep the original and a compatible delivery choice until the receiving workflow is confirmed. In ZipMyImages, local processing keeps source images off a conversion server, but it does not change the browser available encoders.