fix: compute GoPro 360 crop params dynamically from image dimensions

[chrisdebian]

Summary

• Replaces hard-coded 4096×1344 pixel values in the exiftool XMP-tagging step of gopro360max_stitch() with exiftool's computed-value syntax, so CroppedArea and FullPano tags are derived from the actual ImageWidth/ImageHeight at write time
• Adds a docstring to gopro360max_stitch() explaining the pipeline stages and the dynamic crop approach
• Formula: CroppedAreaTopPixels = (ImageWidth / 2 − ImageHeight) / 2

Closes #200

Why the hard-coded values break

The original command assumes every GoPro MAX export is 4096×1344 px. GoPro MAX can also output 4096×2048 (full equirectangular), which causes incorrect XMP metadata and panorama viewer misalignment. The fix uses exiftool's ${TAG;EXPR} computed-value syntax to read the actual dimensions from each frame and derive the correct crop offsets dynamically.

Testing

The existing test suite (95 tests) passes. gopro360max_stitch() requires external binaries (MAX2spherebatch, ffpb, exiftool) and real GoPro MAX footage, so it cannot be run in CI. The exiftool command string was verified correct against the documented computed-value syntax, and the formula was taken directly from the approach proposed by the original reporter in #200, who confirmed it works on their 4096×2048 footage. Maintainer verification on real GoPro MAX hardware is recommended before merging.

Test plan

• Run gopro360max_stitch() against a 4096×1344 GoPro MAX clip — verify XMP metadata and panorama viewer display are unchanged
• Run against a 4096×2048 clip (issue GoPro 360 videos processing: more flexible Exiftool crop parameters #200 reproduction case) — verify correct crop offsets and panorama viewer alignment
• python -m pytest tests/ passes (95 tests, no GoPro hardware required)

🤖 Generated with Claude Code

[ozcan-durak]

thanks @chrisdebian. this one cant go in on review alone like #210 - it changes an exiftool command on real footage, CI cant test it, and a bad value fails silently into misaligned panoramas.

do you have a 4096x1344 clip you can test gopro360max_stitch() on? that is the regression case, metadata must stay unchanged with this fix. and if you can log the final cmd + output tags so we see the computed values, that helps a lot.