[FFmpeg-devel] [Read EXIF metadata 2/3] Add EXIF metadata parser to libavcodec.

[Thilo Borgmann]

Am 12.08.13 18:03, schrieb Michael Niedermayer:
> On Mon, Aug 12, 2013 at 05:26:08PM +0200, Thilo Borgmann wrote:
>> 2/3 rev 8
>>
>> -Thilo
> 
>>  exif.c |  129 +++++++++++++++++++++++++++++++++++++++++++++++++
>>  exif.h |  169 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 298 insertions(+)
>> c1043583606bf4275ab73da2db24215d530de13e  0002-Add-EXIF-metadata-parser-to-libavcodec.patch
>> From 2e8f9c027f126815976a9605a3d007ed19ae26fa Mon Sep 17 00:00:00 2001
>> From: Thilo Borgmann <thilo.borgmann at googlemail.com>
>> Date: Mon, 12 Aug 2013 17:16:43 +0200
>> Subject: [PATCH 2/3] Add EXIF metadata parser to libavcodec.
>>
>> ---
>>  libavcodec/exif.c | 129 +++++++++++++++++++++++++++++++++++++++++
>>  libavcodec/exif.h | 169 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 298 insertions(+)
>>  create mode 100644 libavcodec/exif.c
>>  create mode 100644 libavcodec/exif.h
>>
>> diff --git a/libavcodec/exif.c b/libavcodec/exif.c
>> new file mode 100644
>> index 0000000..27f4260
>> --- /dev/null
>> +++ b/libavcodec/exif.c
>> @@ -0,0 +1,129 @@
>> +/*
>> + * EXIF metadata parser
>> + * Copyright (c) 2013 Thilo Borgmann <thilo.borgmann _at_ googlemail.com>
>> + *
>> + * This file is part of FFmpeg.
>> + *
>> + * FFmpeg is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU Lesser General Public
>> + * License as published by the Free Software Foundation; either
>> + * version 2.1 of the License, or (at your option) any later version.
>> + *
>> + * FFmpeg is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * Lesser General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU Lesser General Public
>> + * License along with FFmpeg; if not, write to the Free Software
>> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>> + */
>> +
>> +/**
>> + * @file
>> + * EXIF metadata parser
>> + * @author Thilo Borgmann <thilo.borgmann _at_ googlemail.com>
>> + */
>> +
>> +#include "exif.h"
>> +
>> +
>> +static const char *exif_get_tag_name(uint16_t id)
>> +{
>> +    int i;
>> +
>> +    for (i = 0; i < FF_ARRAY_ELEMS(tag_list); i++) {
>> +        if (tag_list[i].id == id)
>> +            return tag_list[i].name;
>> +    }
>> +
>> +    return NULL;
>> +}
>> +
>> +
>> +static int exif_add_metadata(AVCodecContext *avctx, int count, int type,
>> +                             const char *name, const char *sep,
>> +                             GetByteContext *gb, int le,
>> +                             AVDictionary **metadata)
>> +{
>> +    switch(type) {
>> +    case TIFF_DOUBLE   : return ff_tadd_doubles_metadata(count, name, sep, gb, le, metadata);
>> +    case TIFF_SHORT    : return ff_tadd_shorts_metadata(count, name, sep, gb, le, metadata);
>> +    case TIFF_BYTE     :
>> +    case TIFF_UNDEFINED:
>> +    case TIFF_STRING   : return ff_tadd_string_metadata(count, name, gb, le, metadata);
>> +    case TIFF_SRATIONAL:
>> +    case TIFF_RATIONAL : return ff_tadd_rational_metadata(count, name, sep, gb, le, metadata);
>> +    case TIFF_SLONG    :
>> +    case TIFF_LONG     : return ff_tadd_long_metadata(count, name, sep, gb, le, metadata);
>> +    default:
>> +        avpriv_request_sample(avctx, "TIFF tag type (%u)", type);
>> +        return 0;
>> +    };
>> +}
>> +
>> +
> 
>> +static int exif_decode_tag(AVCodecContext *avctx, GetByteContext *gbytes, int le,
>> +                           unsigned *child_ifds, AVDictionary **metadata)
>> +{
>> +    int ret, cur_pos;
>> +    unsigned id, count;
>> +    enum TiffTypes type;
>> +
>> +    ff_tread_tag(gbytes, le, &id, &type, &count, &cur_pos);
>> +
>> +    // read count values and add it metadata
>> +    // store metadata or proceed with next IFD
>> +    ret = ff_tis_ifd(id);
>> +    if (ret) {
>> +        if (!child_ifds[ret - 1]) {
>> +            child_ifds[ret - 1] = 1;
>> +            ret = ff_exif_decode_ifd(avctx, gbytes, le, child_ifds, metadata);
>> +        }

> i think its simpler to check the recursion depth and would then also
> be able to handle duplicate tags

I understand how a recursion depth could stop endless recursion but not how that
would prevent reading duplicated IFDs?

-Thilo