macOS上使用qt creator编译调试ffmpeg.c-编程知识

1 前言

上文macOS上将ffmpeg.c编译成Framework介绍了使用xocde将ffmpeg.c编译成Framework的方法，这里列举另外一种办法，就是用qt creator来完成这件事情。

编译环境如下：

qt creator 9.0.2；
ffmpeg release/6.1;

2 编译ffmpeg.c

大致思路如下：

将ffmpeg.c编译成动态库dylib；
在qt creator的app工程里使用该动态库；

值得一提的是，用qt creator新建工程，必须是Plain C Application，不能是C++的工程。因为ffmpeg.c相关头文件的变量名用到了c++的关键字，比如class等，这会导致在c++项目里无法编译成功。

2.1 新建qt工程

新建一个Plain C Application工程，并选择使用cmake来构建项目：

代码目录结构如下图：

2.2 改写ffmpeg.c接口

在ffmpeg.h文件中将main方法名改为ffmpeg：

#将main方法名改为ffmpeg
int ffmpeg(int argc, char* argv[]);

在ffmpeg.c文件中将main方法名改为ffmpeg：

#将main方法名改为ffmpeg
int ffmpeg(int argc, char **argv)
{int ret, err_rate_exceeded;BenchmarkTimeStamps ti;init_dynload();setvbuf(stderr,NULL,_IONBF,0); /* win32 runtime needs this */av_log_set_flags(AV_LOG_SKIP_REPEATED);parse_loglevel(argc, argv, options);#if CONFIG_AVDEVICEavdevice_register_all();
#endifavformat_network_init();show_banner(argc, argv, options);/* parse options and open all input/output files */ret = ffmpeg_parse_options(argc, argv);if (ret < 0)goto finish;if (nb_output_files <= 0 && nb_input_files == 0) {show_usage();av_log(NULL, AV_LOG_WARNING, "Use -h to get full help or, even better, run 'man %s'\n", program_name);ret = 1;goto finish;}if (nb_output_files <= 0) {av_log(NULL, AV_LOG_FATAL, "At least one output file must be specified\n");ret = 1;goto finish;}current_time = ti = get_benchmark_time_stamps();ret = transcode(&err_rate_exceeded);if (ret >= 0 && do_benchmark) {int64_t utime, stime, rtime;current_time = get_benchmark_time_stamps();utime = current_time.user_usec - ti.user_usec;stime = current_time.sys_usec  - ti.sys_usec;rtime = current_time.real_usec - ti.real_usec;av_log(NULL, AV_LOG_INFO,"bench: utime=%0.3fs stime=%0.3fs rtime=%0.3fs\n",utime / 1000000.0, stime / 1000000.0, rtime / 1000000.0);}ret = received_nb_signals ? 255 :err_rate_exceeded   ?  69 : ret;finish:if (ret == AVERROR_EXIT)ret = 0;ffmpeg_cleanup(ret);return ret;
}

2.3 编写CMakeLists.txt

用qt creator编译ffmpeg.c，关键在于cmake脚本的编写，这里贴出所写的cmake编译脚本：

cmake_minimum_required(VERSION 3.5)project(qt-ffmpegc LANGUAGES C)#ffmpeg源码根目录
set(FFMPEG_SRC_ROOT_PATH "/Users/mingo/Applications/workspace/av/ffmpeg")
#fftools源码目录
set(FFMPEG_SRC_TOOL_PATH ${FFMPEG_SRC_ROOT_PATH}/fftools)
#列出要参与编译的ffmpeg.c相关源码
set(FFMPEG_SRC${FFMPEG_SRC_TOOL_PATH}/cmdutils.c ${FFMPEG_SRC_TOOL_PATH}/cmdutils.h${FFMPEG_SRC_TOOL_PATH}/ffmpeg_dec.c ${FFMPEG_SRC_TOOL_PATH}/ffmpeg_demux.c${FFMPEG_SRC_TOOL_PATH}/ffmpeg_enc.c ${FFMPEG_SRC_TOOL_PATH}/ffmpeg_filter.c${FFMPEG_SRC_TOOL_PATH}/ffmpeg_hw.c ${FFMPEG_SRC_TOOL_PATH}/ffmpeg_mux_init.c${FFMPEG_SRC_TOOL_PATH}/ffmpeg_mux.c ${FFMPEG_SRC_TOOL_PATH}/ffmpeg_mux.h${FFMPEG_SRC_TOOL_PATH}/ffmpeg_opt.c ${FFMPEG_SRC_TOOL_PATH}/ffmpeg.c${FFMPEG_SRC_TOOL_PATH}/ffmpeg.h${FFMPEG_SRC_TOOL_PATH}/opt_common.c ${FFMPEG_SRC_TOOL_PATH}/opt_common.h${FFMPEG_SRC_TOOL_PATH}/sync_queue.c ${FFMPEG_SRC_TOOL_PATH}/sync_queue.h${FFMPEG_SRC_TOOL_PATH}/thread_queue.c ${FFMPEG_SRC_TOOL_PATH}/thread_queue.h${FFMPEG_SRC_TOOL_PATH}/objpool.c ${FFMPEG_SRC_TOOL_PATH}/objpool.h)#ffmpeg的头文件、lib文件及相关基础库根目录
set(FFMPEG_BUILD_ROOT_PATH ${FFMPEG_SRC_ROOT_PATH}/mac_build)
#ffmpeg几个库的include文件路径
set(FFMPEG_INCLUDE_PATH ${FFMPEG_BUILD_ROOT_PATH}/include)
#全部的依赖库所在目录
set(FFMPEG_LIB_PATH ${FFMPEG_BUILD_ROOT_PATH}/lib)#系统基础库
set(SYS_BASE_LIB iconv z bz2)
#ffmpeg几个.a库
set(LINK_FFMPEG_LIBS${FFMPEG_LIB_PATH}/libavformat.a${FFMPEG_LIB_PATH}/libavutil.a${FFMPEG_LIB_PATH}/libavcodec.a${FFMPEG_LIB_PATH}/libavfilter.a${FFMPEG_LIB_PATH}/libswscale.a${FFMPEG_LIB_PATH}/libswresample.a${FFMPEG_LIB_PATH}/libavdevice.a)
#其他依赖库
set(OTHER_3RDPARTY_LIBS${FFMPEG_LIB_PATH}/libxcb.a${FFMPEG_LIB_PATH}/libxcb-xfixes.a${FFMPEG_LIB_PATH}/libxcb-shm.a${FFMPEG_LIB_PATH}/libxcb-shape.a${FFMPEG_LIB_PATH}/libXdmcp.a${FFMPEG_LIB_PATH}/libXau.a${FFMPEG_LIB_PATH}/libX11.a${FFMPEG_LIB_PATH}/libX11-xcb.a${FFMPEG_LIB_PATH}/libSDL2.dylib)#将ffmpeg.c打成动态库
add_library(ffmpegc SHARED ${FFMPEG_SRC})
#指定ffmpegc动态库相关依赖库
target_link_libraries(ffmpegc PRIVATE ${LINK_FFMPEG_LIBS} ${OTHER_3RDPARTY_LIBS} ${SYS_BASE_LIB})
#ffmpeg所依赖的macOS的Framework
list(APPEND DEPENDCY_LIB_LISTFoundation AudioToolbox CoreAudio AVFoundation CoreVideo CoreMedia CoreGraphics OpenGL Metal VideoToolbox CoreImage AppKit CoreFoundation CoreServices Security)
foreach(var IN LISTS DEPENDCY_LIB_LIST)target_link_libraries(ffmpegc PRIVATE "-framework ${var}")
endforeach()
# 设置ffmpeg.c动态库的输出路径
set_target_properties(ffmpegc PROPERTIESLIBRARY_OUTPUT_DIRECTORY ${FFMPEG_LIB_PATH}ARCHIVE_OUTPUT_DIRECTORY ${FFMPEG_LIB_PATH}
)add_executable(qt-ffmpegc main.c)include_directories(${FFMPEG_SRC_ROOT_PATH})
include_directories(${FFMPEG_SRC_TOOL_PATH})
include_directories(${FFMPEG_INCLUDE_PATH})#指定qt-ffmpegc app工程所依赖的库，与ffmpeg.c一致
target_link_libraries(qt-ffmpegc PRIVATE ${LINK_FFMPEG_LIBS} ${OTHER_3RDPARTY_LIBS} ${SYS_BASE_LIB})
#qt-ffmpegc依赖ffmpegc动态库
target_link_libraries(qt-ffmpegc PRIVATE ${FFMPEG_LIB_PATH}/libffmpegc.dylib)
#qt-ffmpegc依赖macOS的各framwork
foreach(var IN LISTS DEPENDCY_LIB_LIST)message(STATUS ${var})target_link_libraries(qt-ffmpegc PRIVATE "-framework ${var}")
endforeach()install(TARGETS qt-ffmpegcLIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR})

值得一提的是，cmake脚本里指定对macOS系统Framework的依赖脚本如下，列出范例代码：

target_link_libraries(qt-ffmpegc PRIVATE "-framework Foundation")

好了，cmake脚本编写完成，现在可以编译ffmpeg.c动态库和qt-ffmpegc可执行文件了。

3 使用ffmpeg.c动态库

列出qt-ffmpegc工程main.c的调用代码：

#include <stdio.h>#include "libavformat/avformat.h"
#include "ffmpeg.h"static void test_ffmpeg() {AVFormatContext* ifmt = NULL;const char* filename = "";int ret = avformat_open_input(&ifmt, filename, NULL, NULL);if (ret < 0) {av_log(ifmt, AV_LOG_INFO, "avformat_open_input failed\n");}ret = avformat_find_stream_info(ifmt, NULL);if (ret < 0) {}AVPacket pkt;av_init_packet(&pkt);while (1) {ret = av_read_frame(ifmt, &pkt);if (pkt.stream_index == 1 &&  pkt.flags & AV_PKT_FLAG_KEY) {av_log(ifmt, AV_LOG_INFO, "keyframe\n");}}
}static void test_ffmpeg_cmd(int argc, const char* argv[]) {ffmpeg(argc, argv);
}int main()
{printf("Hello World!\n");test_ffmpeg();const char* args[3] = { "ffmpeg", "-h", "filter=overlay" };test_ffmpeg_cmd(3, args);return 0;
}

然后编译调试，执行ffmpeg -h filter=overlay范例命令：