Add support for decoding input with ffmpeg libs in main (Linux)

- search for ffmpeg at cmake time
- include ffmpegs/libav headers in main.cpp
Todo:
- if needed convert input file to wav 16khz in main.cpp

CMakeLists.txt

@@ -59,6 +59,10 @@ option(WHISPER_BUILD_EXAMPLES         "whisper: build examples" ${WHISPER_STANDA
 
 option(WHISPER_SDL2                   "whisper: support for libSDL2" OFF)
 
+if (CMAKE_SYSTEM_NAME MATCHES "Linux")
+  option(WHISPER_FFMPEG                 "whisper: support building and linking with ffmpeg libs" OFF)
+endif()
+
 option(WHISPER_NO_AVX                 "whisper: disable AVX"         OFF)
 option(WHISPER_NO_AVX2                "whisper: disable AVX2"        OFF)
 option(WHISPER_NO_AVX512              "whisper: disable AVX512"      ON)
@@ -125,6 +129,23 @@ else()
     set(CMAKE_CXX_STANDARD 11)
 endif()
 
+if (WHISPER_FFMPEG)
+  # As today (cmake 3.27), there is no official cmake support for FindFFmpeg. eg: not possible:
+  # find_package(FFmpeg COMPONENTS AVCODEC AVFORMAT AVUTIL AVDEVICE REQUIRED)
+  # Check with reviewers: worth to embed a FindFFmpeg.cmake script in whisper.cpp ?
+  # eg https://github.com/snikulov/cmake-modules/blob/master/FindFFmpeg.cmake
+  # Using PkgConfig atm:
+  find_package(PkgConfig REQUIRED)
+  pkg_check_modules(FFMPEG REQUIRED IMPORTED_TARGET libavdevice libavfilter libavformat libavcodec libswresample libswscale libavutil)
+  if (NOT ${FFMPEG_FOUND})
+    message(FATAL_ERROR "Cannot find ffmpeg libs/headers")
+  endif()
+  message(STATUS "Found ffmpeg headers in: ${FFMPEG_INCLUDE_DIRS}")
+  include_directories(${FFMPEG_INCLUDE_DIRS})
+  add_compile_definitions(WHISPER_FFMPEG)
+  set(WHISPER_EXTRA_LIBS  ${WHISPER_EXTRA_LIBS} PkgConfig::FFMPEG)
+endif()
+
 # on APPLE
 if (APPLE)
     # include Accelerate framework

examples/main/CMakeLists.txt

@@ -3,4 +3,8 @@ add_executable(${TARGET} main.cpp)
 
 include(DefaultTargetOptions)
 
-target_link_libraries(${TARGET} PRIVATE common whisper ${CMAKE_THREAD_LIBS_INIT})
+if (WHISPER_FFMPEG)
+  target_link_libraries(${TARGET} PRIVATE common whisper ${CMAKE_THREAD_LIBS_INIT} PkgConfig::FFMPEG)
+else()
+  target_link_libraries(${TARGET} PRIVATE common whisper ${CMAKE_THREAD_LIBS_INIT})
+endif()

examples/main/main.cpp

@@ -3,6 +3,12 @@
 #include "whisper.h"
 #include "grammar-parser.h"
 
+#ifdef WHISPER_FFMPEG
+  #include <libavutil/frame.h>
+  #include <libavutil/mem.h>
+  #include <libavcodec/avcodec.h>
+#endif
+
 #include <cmath>
 #include <fstream>
 #include <cstdio>