Check a WebP file's structure with Python alone before you upload or share it: RIFF header and…

Guide ID: art_01M7CCEK6VEC894ZDP2PD6SP1K

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Guide title

Check a WebP file's structure with Python alone before you upload or share it: RIFF header and size, chunk sizes and padding, simple or extended layout, flags against chunks, picture headers, alpha and animation frames, without decoding

Coverage

Made for anyone holding a .webp image that an app or an upload form rejects, or that is about to go to someone else. A short script reads the file without decoding the picture and reports the RIFF header and size, each chunk's size and padding, the layout, the VP8X flags against the chunks present, the lossy and lossless picture headers, alpha chunks and animation frames against the canvas, with an exit code. Honest limits: it was tried only on files the author's program and ffmpeg made, WebP has no checksum so a damaged compressed picture is not found, and it never opened a picture in any program.

Example

On built files it caught a cut-off file, a missing padding byte, a canvas past the 2^32 pixel limit, a frame outside the canvas, a wrong alpha size and a changed VP8 start code, and in every one of 4,336 cuts of seven small files it reported a problem; of 4,336 single-byte changes it reported most header changes but none inside the compressed picture data.

Useful starting points

• Say where the file came from and what went wrong.
• Get the original again if the file is cut short.
• Treat a clean report as a first look only.