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avcodec/exif: parse additional EXIF IFDs

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Most EXIF metadata is in IFD0 and most EXIF payloads only contain
one IFD, but it is possible for there to be more IFDs after the
existing trailing one. exiftool and similar software report these IFDs
as IFD1, IFD2, etc. This commit reads those additional IFDs and attaches
them as dummy entries in the top-level IFD ranging from 0xFFFC down to
0xFFED, which are unused by the EXIF spec. The EXIF API is only able to
return and work with a single IFD, so by attaching it as a subdirectory
this metadata can be preserved.

This is done transparently through the read/write process. Upon parsing
an additional IFD1, it will be attached, but it will be written with
av_exif_write after IFD0 rather than as a subdirectory, as intended.

Existing files without more than one IFD, i.e. most files, will be unaffected
by this change, as well as API clients looking to parse specific fields, but
now more metadata is parsed and written, rather than simply being discarded
as trailing data.

Signed-off-by: Leo Izen <leo.izen@gmail.com>
This commit is contained in:
Leo Izen
2025-11-30 06:55:16 -05:00
parent 105b6fcd9c
commit 784aa09fa8
4 changed files with 137 additions and 12 deletions
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111
libavcodec/exif.c
View File

@@ -192,6 +192,24 @@ static const struct exif_tag tag_list[] = { // JEITA CP-3451 EXIF specification:
{"InteropIFD", 0xA005}, // <- Table 13 Interoperability IFD Attribute Information
{"GlobalParametersIFD", 0x0190},
{"ProfileIFD", 0xc6f5},
/* Extra FFmpeg tags */
{ "IFD1", 0xFFFC},
{ "IFD2", 0xFFFB},
{ "IFD3", 0xFFFA},
{ "IFD4", 0xFFF9},
{ "IFD5", 0xFFF8},
{ "IFD6", 0xFFF7},
{ "IFD7", 0xFFF6},
{ "IFD8", 0xFFF5},
{ "IFD9", 0xFFF4},
{ "IFD10", 0xFFF3},
{ "IFD11", 0xFFF2},
{ "IFD12", 0xFFF1},
{ "IFD13", 0xFFF0},
{ "IFD14", 0xFFEF},
{ "IFD15", 0xFFEE},
{ "IFD16", 0xFFED},
};
/* same as type_sizes but with string == 1 */
@@ -655,7 +673,9 @@ static size_t exif_get_ifd_size(const AVExifMetadata *ifd)
for (size_t i = 0; i < ifd->count; i++) {
const AVExifEntry *entry = &ifd->entries[i];
if (entry->type == AV_TIFF_IFD) {
total_size += BASE_TAG_SIZE + exif_get_ifd_size(&entry->value.ifd) + entry->ifd_offset;
/* this is an extra IFD, not an entry, so we don't need to add base tag size */
size_t base_size = entry->id > 0xFFECu && entry->id <= 0xFFFCu ? 0 : BASE_TAG_SIZE;
total_size += base_size + exif_get_ifd_size(&entry->value.ifd) + entry->ifd_offset;
} else {
size_t payload_size = entry->count * exif_sizes[entry->type];
total_size += BASE_TAG_SIZE + (payload_size > 4 ? payload_size : 0);
@@ -728,12 +748,16 @@ int av_exif_write(void *logctx, const AVExifMetadata *ifd, AVBufferRef **buffer,
AVBufferRef *buf = NULL;
size_t size, headsize = 8;
PutByteContext pb;
int ret, off = 0;
int ret = 0, off = 0, next;
AVExifMetadata *ifd_new = NULL;
AVExifMetadata extra_ifds[16] = { 0 };
int le = 1;
if (*buffer)
return AVERROR(EINVAL);
if (*buffer) {
ret = AVERROR(EINVAL);
goto end;
}
size = exif_get_ifd_size(ifd);
switch (header_mode) {
@@ -753,8 +777,10 @@ int av_exif_write(void *logctx, const AVExifMetadata *ifd, AVBufferRef **buffer,
break;
}
buf = av_buffer_alloc(size + off + headsize);
if (!buf)
return AVERROR(ENOMEM);
if (!buf) {
ret = AVERROR(ENOMEM);
goto end;
}
if (header_mode == AV_EXIF_EXIF00) {
AV_WL32(buf->data, MKTAG('E','x','i','f'));
@@ -772,16 +798,63 @@ int av_exif_write(void *logctx, const AVExifMetadata *ifd, AVBufferRef **buffer,
tput32(&pb, le, 8);
}
int extras;
for (extras = 0; extras < FF_ARRAY_ELEMS(extra_ifds); extras++) {
AVExifEntry *extra_entry = NULL;
uint16_t extra_tag = 0xFFFCu - extras;
ret = av_exif_get_entry(logctx, (AVExifMetadata *) ifd, extra_tag, 0, &extra_entry);
if (ret <= 0)
break;
av_log(logctx, AV_LOG_DEBUG, "found extra IFD tag: %04x\n", extra_tag);
if (!ifd_new) {
ifd_new = av_exif_clone_ifd(ifd);
if (!ifd_new)
break;
ifd = ifd_new;
}
/* calling remove_entry will call av_exif_free on the original */
AVExifMetadata *cloned = av_exif_clone_ifd(&extra_entry->value.ifd);
if (!cloned)
break;
extra_ifds[extras] = *cloned;
/* don't use av_exif_free here, we want to preserve internals */
av_free(cloned);
ret = av_exif_remove_entry(logctx, ifd_new, extra_tag, 0);
if (ret < 0)
break;
}
next = bytestream2_tell_p(&pb);
ret = exif_write_ifd(logctx, &pb, le, 0, ifd);
if (ret < 0) {
av_buffer_unref(&buf);
av_log(logctx, AV_LOG_ERROR, "error writing EXIF data: %s\n", av_err2str(ret));
return ret;
}
next += ret;
for (int i = 0; i < extras; i++) {
av_log(logctx, AV_LOG_DEBUG, "writing additional ifd at: %d\n", next);
/* exif_write_ifd always writes 0 i.e. last ifd so we overwrite that here */
bytestream2_seek_p(&pb, -4, SEEK_CUR);
tput32(&pb, le, next);
bytestream2_seek_p(&pb, next, SEEK_SET);
ret = exif_write_ifd(logctx, &pb, le, 0, &extra_ifds[i]);
if (ret < 0)
break;
next += ret;
}
*buffer = buf;
ret = 0;
return 0;
end:
av_exif_free(ifd_new);
av_freep(&ifd_new);
for (int i = 0; i < FF_ARRAY_ELEMS(extra_ifds); i++)
av_exif_free(&extra_ifds[i]);
return ret;
}
int av_exif_parse_buffer(void *logctx, const uint8_t *buf, size_t size,
@@ -839,8 +912,30 @@ int av_exif_parse_buffer(void *logctx, const uint8_t *buf, size_t size,
av_log(logctx, AV_LOG_ERROR, "error decoding EXIF data: %s\n", av_err2str(ret));
return ret;
}
if (!ret)
goto finish;
int next = ret;
bytestream2_seek(&gbytes, next, SEEK_SET);
return bytestream2_tell(&gbytes);
/* cap at 16 extra IFDs for sanity/parse security */
for (int extra_tag = 0xFFFCu; extra_tag > 0xFFECu; extra_tag--) {
AVExifMetadata extra_ifd = { 0 };
ret = exif_parse_ifd_list(logctx, &gbytes, le, 0, &extra_ifd, 1);
if (ret < 0) {
av_exif_free(&extra_ifd);
break;
}
next = ret;
av_log(logctx, AV_LOG_DEBUG, "found extra IFD: %04x with next=%d\n", extra_tag, ret);
bytestream2_seek(&gbytes, next, SEEK_SET);
ret = av_exif_set_entry(logctx, ifd, extra_tag, AV_TIFF_IFD, 1, NULL, 0, &extra_ifd);
av_exif_free(&extra_ifd);
if (ret < 0 || !next || bytestream2_get_bytes_left(&gbytes) <= 0)
break;
}
finish:
return bytestream2_tell(&gbytes) + off;
}
#define COLUMN_SEP(i, c) ((i) ? ((i) % (c) ? ", " : "\n") : "")

8
tests/ref/fate/exif-image-jpg
View File

@@ -197,6 +197,12 @@ TAG:ExifIFD/ExposureMode= 0
TAG:ExifIFD/WhiteBalance= 0
TAG:ExifIFD/DigitalZoomRatio= 4000:4000
TAG:ExifIFD/SceneCaptureType= 0
TAG:IFD1/Compression= 6
TAG:IFD1/XResolution= 180:1
TAG:IFD1/YResolution= 180:1
TAG:IFD1/ResolutionUnit= 2
TAG:IFD1/JPEGInterchangeFormat= 5108
TAG:IFD1/JPEGInterchangeFormatLength= 4214
[SIDE_DATA]
side_data_type=3x3 displaymatrix
displaymatrix=
@@ -208,6 +214,6 @@ rotation=0
[/SIDE_DATA]
[SIDE_DATA]
side_data_type=EXIF metadata
size=3285
size=3379
[/SIDE_DATA]
[/FRAME]

8
tests/ref/fate/exif-image-webp
View File

@@ -197,6 +197,12 @@ TAG:ExifIFD/ExposureMode= 0
TAG:ExifIFD/WhiteBalance= 0
TAG:ExifIFD/DigitalZoomRatio= 4000:4000
TAG:ExifIFD/SceneCaptureType= 0
TAG:IFD1/Compression= 6
TAG:IFD1/XResolution= 180:1
TAG:IFD1/YResolution= 180:1
TAG:IFD1/ResolutionUnit= 2
TAG:IFD1/JPEGInterchangeFormat= 5108
TAG:IFD1/JPEGInterchangeFormatLength= 4214
[SIDE_DATA]
side_data_type=3x3 displaymatrix
displaymatrix=
@@ -208,6 +214,6 @@ rotation=0
[/SIDE_DATA]
[SIDE_DATA]
side_data_type=EXIF metadata
size=3285
size=3379
[/SIDE_DATA]
[/FRAME]

22
tests/ref/fate/mov-heic-demux-still-image-multiple-thumb
View File

@@ -1895,9 +1895,27 @@ TAG:ExifIFD/0xA434=LUMIX S 24-60/F2.8
TAG:0x9006= 39936
TAG:0x9007= 65536
TAG:0x9008= 272401
TAG:IFD1/Compression= 6
TAG:IFD1/StripOffsets= 106496
TAG:IFD1/Orientation= 1
TAG:IFD1/XResolution= 180:1
TAG:IFD1/YResolution= 180:1
TAG:IFD1/ResolutionUnit= 2
TAG:IFD1/JPEGInterchangeFormat= 106496
TAG:IFD1/JPEGInterchangeFormatLength= 20480
TAG:IFD1/YCbCrPositioning= 2
TAG:IFD2/Compression= 6
TAG:IFD2/StripOffsets= 126976
TAG:IFD2/Orientation= 1
TAG:IFD2/XResolution= 180:1
TAG:IFD2/YResolution= 180:1
TAG:IFD2/ResolutionUnit= 2
TAG:IFD2/JPEGInterchangeFormat= 126976
TAG:IFD2/JPEGInterchangeFormatLength= 858544
TAG:IFD2/YCbCrPositioning= 2
[SIDE_DATA]
side_data_type=EXIF metadata
size=30308
size=30568
[/SIDE_DATA]
[SIDE_DATA]
side_data_type=H.26[45] User Data Unregistered SEI message
@@ -1927,7 +1945,7 @@ DISPOSITION:still_image=0
DISPOSITION:multilayer=0
[SIDE_DATA]
side_data_type=EXIF metadata
size=30308
size=30568
[/SIDE_DATA]
[/STREAM]
[STREAM]