meson: Rework FFmpeg / tinycompress detection and add pw-cat-ffmpeg option

* Decouple FFmpeg integration in pw-cat from the ffmpeg option; if
  one wants to use Compress-Offload but not the ffmpeg SPA plugin,
  it is then possible to just pass -Dpw-cat-ffmpeg=enabled to meson.
  Likewise, this also makes it possible to build the ffmpeg plugin
  without extending pw-cat.
* tinycompress does not need to be detected in the root meson.build,
  since it is only needed by the alsa plugin.

meson.build

@@ -266,14 +266,17 @@ if not readline_dep.found()
   readline_dep = cc.find_library('readline', required : get_option('readline'))
 endif
 
-need_avcodec = get_option('ffmpeg').enabled() or get_option('pw-cat').enabled()
-avcodec_dep = dependency('libavcodec', required: need_avcodec)
-avformat_dep = dependency('libavformat', required: get_option('pw-cat'))
-summary({'Libav for pw-cat': avcodec_dep.found() and avformat_dep.found()}, bool_yn: true, section: 'Support for ALSA Compress-Offload API')
-tinycompress_dep = cc.find_library('tinycompress', has_headers: ['tinycompress/tinycompress.h' ], required: get_option('compress-offload'))
-summary({'Compress-Offload sink': tinycompress_dep.found()}, bool_yn: true, section: 'Support for ALSA Compress-Offload API')
-compress_offload_enabled = avcodec_dep.found() and avformat_dep.found() and tinycompress_dep.found()
-cdata.set('HAVE_ALSA_COMPRESS_OFFLOAD', compress_offload_enabled)
+# Both the FFmpeg SPA plugin and the pw-cat FFmpeg integration use libavcodec.
+# But only the latter also needs libavformat.
+# Search for these libraries here, globally, so both of these subprojects can reuse the results.
+pw_cat_ffmpeg = get_option('pw-cat-ffmpeg')
+ffmpeg = get_option('ffmpeg')
+if pw_cat_ffmpeg.allowed() or ffmpeg.allowed()
+  avcodec_dep = dependency('libavcodec', required: pw_cat_ffmpeg.enabled() or ffmpeg.enabled())
+  avformat_dep = dependency('libavformat', required: pw_cat_ffmpeg.enabled())
+else
+  avcodec_dep = dependency('', required: false)
+endif
 
 summary({'readline (for pw-cli)': readline_dep.found()}, bool_yn: true, section: 'Misc dependencies')
 cdata.set('HAVE_READLINE', readline_dep.found())

meson_options.txt

@@ -188,6 +188,10 @@ option('pw-cat',
        description: 'Build pw-cat/pw-play/pw-record',
        type: 'feature',
        value: 'auto')
+option('pw-cat-ffmpeg',
+       description: 'Enable FFmpeg integration in pw-cat/pw-play/pw-record',
+       type: 'feature',
+       value: 'disabled')
 option('udev',
        description: 'Enable Udev integration',
        type: 'feature',

spa/meson.build

@@ -83,6 +83,10 @@ if get_option('spa-plugins').allowed()
   libcamera_dep = dependency('libcamera', required: get_option('libcamera'))
   summary({'libcamera': libcamera_dep.found()}, bool_yn: true, section: 'Backend')
 
+  tinycompress_dep = cc.find_library('tinycompress', has_headers: ['tinycompress/tinycompress.h' ], required: get_option('compress-offload'))
+  summary({'Compress-Offload': tinycompress_dep.found()}, bool_yn: true, section: 'Backend')
+  cdata.set('HAVE_ALSA_COMPRESS_OFFLOAD', tinycompress_dep.found())
+
   # common dependencies
   libudev_dep = dependency('libudev', required: alsa_dep.found() or get_option('udev').enabled() or get_option('v4l2').enabled())
   summary({'Udev': libudev_dep.found()}, bool_yn: true, section: 'Backend')

src/tools/meson.build

@@ -32,15 +32,18 @@ if ncurses_dep.found()
 endif
 
 build_pw_cat = false
+build_pw_cat_with_ffmpeg = false
 pwcat_deps = [ sndfile_dep ]
-if avcodec_dep.found() and avformat_dep.found()
-  pwcat_deps += avcodec_dep
-  pwcat_deps += avformat_dep
-endif
 
 if get_option('pw-cat').allowed() and sndfile_dep.found()
   build_pw_cat = true
 
+  if pw_cat_ffmpeg.allowed() and avcodec_dep.found() and avformat_dep.found()
+    pwcat_deps += avcodec_dep
+    pwcat_deps += avformat_dep
+    build_pw_cat_with_ffmpeg = true
+  endif
+
   pwcat_sources = [
     'pw-cat.c',
     'midifile.c',
@@ -70,6 +73,9 @@ elif not sndfile_dep.found() and get_option('pw-cat').enabled()
   error('pw-cat is enabled but required dependency `sndfile` was not found.')
 endif
 summary({'Build pw-cat tool': build_pw_cat}, bool_yn: true, section: 'pw-cat/pw-play/pw-dump tool')
+if build_pw_cat
+  summary({'Build pw-cat with FFmpeg integration': build_pw_cat_with_ffmpeg}, bool_yn: true, section: 'pw-cat/pw-play/pw-dump tool')
+endif
 
 if dbus_dep.found()
   executable('pw-reserve',