On 9/16/2024 11:43 AM, Leo Izen wrote:
I've made some changes to the last EXIF overhaul patch I sent, notably I fixed up some bugs and added MakerNote parsing, so it should not corrupt MakerNotes that are inside TIFF files.MakerNote is supposed to be a binary blob but many camera manufacturers treat it as an IFD (e.g. Canon) with offsets relative to the start of the file, so it has to be parsed in order to move it from TIFF to another file or it will be corrupted. I also fixed the fate tests now that pngenc.c writes eXIf chunks, so those should pass. I haven't come up with a solution that Andreas proposed, which is:If I see this correctly, then these patches can lead to a situation where an input packet has rotation metadata in exif which gets exported twice -- as displaymatrix and as exif metadata side data. If the user changes the displaymatrix (e.g. applies the transformation to the image data and removes the displaymatrix side data before reencoding), the exif data (that the user would probably not be aware of) would still be there and get propagated into the output, corrupting it.Zeroing out the EXIF orientation tag upon attaching the displaymatrix is something I did consider, but it would corrupt encoding unless I also read the displaymatrix data and attach it as EXIF orientation. This isn't too hard if the Orientation tag exists but it's more difficult if it doesn't already exist. It's also not clear what to do if the AVDisplayMatrix is not in the dihedral group D4. Currently there's no code that takes an AVDictionary and writes it back into EXIF as these are not compatible structures. EXIF includes integers of varying lengths, while AVDictionary contains strings only.
Conversion from AVDictionary to coded EXIF metadata would be lossy anyway because of the double type. What you could do i guess is write a function that removes a given entry from a raw EXIF buffer.
Leo Izen (3): various: change EXIF metadata into AVFrameSideData avcodec/pngdec: parse eXIf chunk avcodec/pngenc: write eXIf chunks fftools/ffprobe.c | 27 +- libavcodec/Makefile | 1 + libavcodec/exif.c | 394 +++++++++++++++++++++-- libavcodec/exif.h | 32 +- libavcodec/exif_internal.h | 55 ++++ libavcodec/mjpegdec.c | 91 +----- libavcodec/mjpegdec.h | 2 +- libavcodec/pngdec.c | 35 ++ libavcodec/pngenc.c | 4 + libavcodec/tiff.c | 19 +- libavcodec/tiff.h | 1 + libavcodec/version.h | 2 +- libavcodec/webp.c | 38 +-- libavformat/avidec.c | 4 +- libavutil/frame.c | 2 + libavutil/frame.h | 6 + tests/ref/fate/cover-art-mp3-id3v2-remux | 6 +- tests/ref/fate/exif-image-embedded | 5 +- tests/ref/fate/exif-image-jpg | 91 +++--- tests/ref/fate/exif-image-webp | 91 +++--- tests/ref/fate/mov-cover-image | 6 +- 21 files changed, 676 insertions(+), 236 deletions(-) create mode 100644 libavcodec/exif_internal.h
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