build: ffmpeg 8 support (AcademySoftwareFoundation#4870)

* Try a build against ffmpeg 8 -- seems to work out of the box, so
document that we support that version in INSTALL.md.
* Augment FindFFmpeg.cmake to correctly identify 7.1 and 8.0 by the very
non-intuitive versioning scheme of ffmpeg's headers.
* Add a FFMPEG_EXTRA_LIBRARIES variable to FindFFmpeg.cmake to allow us
to easily inject extra library dependencies (coincidentally, I need this
at work to force it to use static libraries).

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

INSTALL.md

@@ -49,7 +49,7 @@ NEW or CHANGED MINIMUM dependencies since the last major release are **bold**.
  * If you want support for camera "RAW" formats:
      * LibRaw >= 0.20 (tested though 0.21.4 and master)
  * If you want support for a wide variety of video formats:
-     * ffmpeg >= 4.0 (tested through 7.1)
+     * ffmpeg >= 4.0 (tested through 8.0)
  * If you want support for jpeg 2000 images:
      * OpenJpeg >= 2.0 (tested through 2.5.3; we recommend 2.4 or higher
        for multithreading support)

src/cmake/modules/FindFFmpeg.cmake

@@ -73,7 +73,11 @@ if (FFMPEG_INCLUDES)
        REGEX "^#define LIBAVCODEC_VERSION_MICRO .*$")
   string (REGEX MATCHALL "[0-9]+[.0-9]+" LIBAVCODEC_VERSION_MICRO "${TMP}")
   set (LIBAVCODEC_VERSION "${LIBAVCODEC_VERSION_MAJOR}.${LIBAVCODEC_VERSION_MINOR}.${LIBAVCODEC_VERSION_MICRO}")
-  if (LIBAVCODEC_VERSION VERSION_GREATER_EQUAL 61.3.100)
+  if (LIBAVCODEC_VERSION VERSION_GREATER_EQUAL 62.11.100)
+      set (FFMPEG_VERSION 8.0)
+  elseif (LIBAVCODEC_VERSION VERSION_GREATER_EQUAL 61.19.101)
+      set (FFMPEG_VERSION 7.1)
+  elseif (LIBAVCODEC_VERSION VERSION_GREATER_EQUAL 61.3.100)
       set (FFMPEG_VERSION 7.0)
   elseif (LIBAVCODEC_VERSION VERSION_GREATER_EQUAL 60.31.102)
       set (FFMPEG_VERSION 6.1)
@@ -130,6 +134,7 @@ if (FFmpeg_FOUND)
       ${FFMPEG_LIBAVFORMAT}
       ${FFMPEG_LIBAVUTIL}
       ${FFMPEG_LIBSWSCALE}
+      ${FFMPEG_EXTRA_LIBRARIES}
     )
 endif ()