Thumbnails lessons from oc10

Previous pain or ideas around this topic…

original comment on [this issue ](https://github.com/owncloud/ocis/issues/10)by @michaelstingl

- Aspect ratio / scale options https://github.com/owncloud/core/issues/16250 , https://github.com/owncloud/core/issues/31268
- Etag for previews https://github.com/owncloud/core/issues/35029
- Share thumbnails? https://github.com/owncloud/core/issues/31855
- Run async / in background https://github.com/owncloud/core/issues/11685
- Discussion around supported file/MIME types https://github.com/owncloud/core/issues/13647 , https://github.com/owncloud/core/issues/31267 , https://github.com/owncloud/ocis/issues/7405
- Multiple thumbnails services for different file types https://github.com/owncloud/core/issues/24424, https://github.com/owncloud/core/issues/24480
- Properly EXIF orientation parameters https://github.com/owncloud/ocis/issues/10#issuecomment-552496876
- Extract thumbnails embedded in EXIF https://github.com/owncloud/core/issues/7232
- Support for modern media formats like [`HEIC` (High Efficiency Image Coding)](https://en.wikipedia.org/wiki/High_Efficiency_Image_File_Format) and [`HEVC` (High Efficiency Video Coding)](https://en.wikipedia.org/wiki/High_Efficiency_Video_Coding), https://github.com/owncloud/core/pull/30093, https://github.com/owncloud/gallery/issues/737, https://github.com/owncloud/ios-legacy/issues/933