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ffmpeg/libavcodec/mjpeg.h
Martin Storsjö d66c52c2b3 Add support for building shared libraries with MSVC 
This requires the makedef perl script by Derek, from the
c89-to-c99 repo. That scripts produces a .def file, listing
the symbols to be exported, based on the gcc version scripts
and the built object files.

To properly load non-function symbols from DLL files, the
data symbol declarations need to have the attribute
__declspec(dllimport) when building the calling code. (On mingw,
the linker can fix this up automatically, which is why it has not
been an issue so far. If this attribute is omitted, linking
actually succeeds, but reads from the table will not produce the
desired results at runtime.)

MSVC seems to manage to link DLLs (and run properly) even if
this attribute is present while building the library itself
(which normally isn't recommended) - other object files in the
same library manage to link to the symbol (with a small warning
at link time, like "warning LNK4049: locally defined symbol
_avpriv_mpa_bitrate_tab imported" - it doesn't seem to be possible
to squelch this warning), and the definition of the tables
themselves produce a warning that can be squelched ("warning C4273:
'avpriv_mpa_bitrate_tab' : inconsistent dll linkage, see previous
definition of 'avpriv_mpa_bitrate_tab').

In this setup, mingw isn't able to link object files that refer to
data symbols with __declspec(dllimport) without those symbols
actually being linked via a DLL (linking avcodec.dll ends up with
errors like "undefined reference to `__imp__avpriv_mpa_freq_tab'").
The dllimport declspec isn't needed at all in mingw, so we simply
choose not to declare it for other compilers than MSVC that requires
it. (If ICL support later requires it, the condition can be extended
later to include both of them.)

This also implies that code that is built to link to a certain
library as a DLL can't link to the same library as a static library.
Therefore, we only allow building either static or shared but not
both at the same time. (That is, static libraries as such can be,
and actually are, built - this is used for linking the test tools to
internal symbols in the libraries - but e.g. libavformat built to
link to libavcodec as a DLL cannot link statically to libavcodec.)

Also, linking to DLLs is slightly different from linking to shared
libraries on other platforms. DLLs use a thing called import
libraries, which is basically a stub library allowing the linker
to know which symbols exist in the DLL and what name the DLL will
have at runtime.

In mingw/gcc, the import library is usually named libfoo.dll.a,
which goes next to a static library named libfoo.a. This allows
gcc to pick the dynamic one, if available, from the normal -lfoo
switches, just as it does for libfoo.a vs libfoo.so on Unix. On
MSVC however, you need to literally specify the name of the import
library instead of the static library.

Signed-off-by: Martin Storsjö <martin@martin.st>
2012-10-18 14:26:15 +03:00

156 lines
4.7 KiB
C
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/*
* MJPEG encoder and decoder
* Copyright (c) 2000, 2001 Fabrice Bellard
* Copyright (c) 2003 Alex Beregszaszi
* Copyright (c) 2003-2004 Michael Niedermayer
*
* Support for external huffman table, various fixes (AVID workaround),
* aspecting, new decode_frame mechanism and apple mjpeg-b support
* by Alex Beregszaszi
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* MJPEG encoder and decoder.
*/
#ifndef AVCODEC_MJPEG_H
#define AVCODEC_MJPEG_H
#include "avcodec.h"
#include "put_bits.h"
/* JPEG marker codes */
typedef enum {
/* start of frame */
SOF0 = 0xc0, /* baseline */
SOF1 = 0xc1, /* extended sequential, huffman */
SOF2 = 0xc2, /* progressive, huffman */
SOF3 = 0xc3, /* lossless, huffman */
SOF5 = 0xc5, /* differential sequential, huffman */
SOF6 = 0xc6, /* differential progressive, huffman */
SOF7 = 0xc7, /* differential lossless, huffman */
JPG = 0xc8, /* reserved for JPEG extension */
SOF9 = 0xc9, /* extended sequential, arithmetic */
SOF10 = 0xca, /* progressive, arithmetic */
SOF11 = 0xcb, /* lossless, arithmetic */
SOF13 = 0xcd, /* differential sequential, arithmetic */
SOF14 = 0xce, /* differential progressive, arithmetic */
SOF15 = 0xcf, /* differential lossless, arithmetic */
DHT = 0xc4, /* define huffman tables */
DAC = 0xcc, /* define arithmetic-coding conditioning */
/* restart with modulo 8 count "m" */
RST0 = 0xd0,
RST1 = 0xd1,
RST2 = 0xd2,
RST3 = 0xd3,
RST4 = 0xd4,
RST5 = 0xd5,
RST6 = 0xd6,
RST7 = 0xd7,
SOI = 0xd8, /* start of image */
EOI = 0xd9, /* end of image */
SOS = 0xda, /* start of scan */
DQT = 0xdb, /* define quantization tables */
DNL = 0xdc, /* define number of lines */
DRI = 0xdd, /* define restart interval */
DHP = 0xde, /* define hierarchical progression */
EXP = 0xdf, /* expand reference components */
APP0 = 0xe0,
APP1 = 0xe1,
APP2 = 0xe2,
APP3 = 0xe3,
APP4 = 0xe4,
APP5 = 0xe5,
APP6 = 0xe6,
APP7 = 0xe7,
APP8 = 0xe8,
APP9 = 0xe9,
APP10 = 0xea,
APP11 = 0xeb,
APP12 = 0xec,
APP13 = 0xed,
APP14 = 0xee,
APP15 = 0xef,
JPG0 = 0xf0,
JPG1 = 0xf1,
JPG2 = 0xf2,
JPG3 = 0xf3,
JPG4 = 0xf4,
JPG5 = 0xf5,
JPG6 = 0xf6,
SOF48 = 0xf7, ///< JPEG-LS
LSE = 0xf8, ///< JPEG-LS extension parameters
JPG9 = 0xf9,
JPG10 = 0xfa,
JPG11 = 0xfb,
JPG12 = 0xfc,
JPG13 = 0xfd,
COM = 0xfe, /* comment */
TEM = 0x01, /* temporary private use for arithmetic coding */
/* 0x02 -> 0xbf reserved */
} JPEG_MARKER;
static inline void put_marker(PutBitContext *p, int code)
{
put_bits(p, 8, 0xff);
put_bits(p, 8, code);
}
#define PREDICT(ret, topleft, top, left, predictor)\
switch(predictor){\
case 1: ret= left; break;\
case 2: ret= top; break;\
case 3: ret= topleft; break;\
case 4: ret= left + top - topleft; break;\
case 5: ret= left + ((top - topleft)>>1); break;\
case 6: ret= top + ((left - topleft)>>1); break;\
default:\
case 7: ret= (left + top)>>1; break;\
}
extern av_export const uint8_t avpriv_mjpeg_bits_dc_luminance[];
extern av_export const uint8_t avpriv_mjpeg_val_dc[];
extern av_export const uint8_t avpriv_mjpeg_bits_dc_chrominance[];
extern av_export const uint8_t avpriv_mjpeg_bits_ac_luminance[];
extern av_export const uint8_t avpriv_mjpeg_val_ac_luminance[];
extern av_export const uint8_t avpriv_mjpeg_bits_ac_chrominance[];
extern av_export const uint8_t avpriv_mjpeg_val_ac_chrominance[];
void ff_mjpeg_build_huffman_codes(uint8_t *huff_size, uint16_t *huff_code,
const uint8_t *bits_table,
const uint8_t *val_table);
#endif /* AVCODEC_MJPEG_H */
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