Support audio_format=caf for AnkiMobile (#120)

* Support `audio_format=caf` for AnkiMobile

* update subs2srs.conf

* add a note about caf
---------

Co-authored-by: Ren Tatsumoto <[email protected]>

.github/RELEASE/subs2srs.conf

@@ -199,9 +199,12 @@ animated_snapshot_quality=5
 ##
 
 # Audio format.
-# Do not switch to `mp3` unless your computer doesn't support `opus`.
+# Opus is the recommended format.
+# It may be required to use a different format when Opus is not supported.
+# This is the case on certain computers or devices which are running proprietary operating systems.
 audio_format=opus
 #audio_format=mp3
+#audio_format=caf
 
 # Sane values are 16k-32k for opus, 64k-128k for mp3.
 audio_bitrate=24k

README.md

@@ -195,6 +195,13 @@ set `audio_format` to `mp3` and/or `snapshot_format` to `jpg`.
 Otherwise, I recommend sticking with `opus` and `webp`,
 as they greatly reduce the size of the generated files.
 
+If you still use AnkiMobile (the [proprietary](https://www.gnu.org/proprietary/) Anki app),
+set `audio_format` to [caf](https://en.wikipedia.org/wiki/Core_Audio_Format) for compatibility.
+The resulting files will use `Opus` as the coding format and Apple's Core Audio
+format as the container format, but will still have the `.ogg` extension to make
+it easier to open in media players because the `.caf` extension is not commonly
+recognized.
+
 If no matter what mpvacious fails to create audio clips and/or snapshots,
 change `use_ffmpeg` to `yes`.
 By using ffmpeg instead of the encoder built in mpv you can work around most encoder issues.

cfg_mgr.lua

@@ -22,7 +22,9 @@ local default_profile_filename = 'subs2srs'
 local profiles_filename = 'subs2srs_profiles'
 
 local function set_audio_format()
-    if self.config.audio_format == 'opus' then
+    if self.config.audio_format == 'opus' or self.config.audio_format == 'caf' then
+        -- https://opus-codec.org/
+        -- https://en.wikipedia.org/wiki/Core_Audio_Format
         self.config.audio_codec = 'libopus'
         self.config.audio_extension = '.ogg'
     else

encoder.lua

@@ -164,6 +164,7 @@ ffmpeg.make_audio_args = function(source_path, output_path, start_timestamp, end
         '-map', string.format("0:%s", tostring(audio_track_id)),
         '-ac', '1',
         '-codec:a', self.config.audio_codec,
+        '-f', self.config.audio_format,
         '-vbr', 'on',
         '-compression_level', '10',
         '-application', 'voip',
@@ -244,6 +245,7 @@ mpv.make_audio_args = function(source_path, output_path, start_timestamp, end_ti
         '--oacopts-add=application=voip',
         '--oacopts-add=compression_level=10',
         table.concat { '--oac=', self.config.audio_codec },
+        table.concat { '--of=', self.config.audio_format },
         table.concat { '--start=', toms(start_timestamp), },
         table.concat { '--end=', toms(end_timestamp), },
         table.concat { '--aid=', audio_track_id },

utils/forvo.lua

@@ -42,6 +42,7 @@ local function reencode(source_path, dest_path)
         '--oacopts-add=compression_level=10',
         '--af-append=silenceremove=1:0:-50dB',
         table.concat { '--oac=', self.config.audio_codec },
+        table.concat { '--of=', self.config.audio_format },
         table.concat { '--oacopts-add=b=', self.config.audio_bitrate },
         table.concat { '-o=', dest_path }
     }