patch MediaWiki extension TimedMediaHandler enable alpha transcodes REL1_43

ext-TimedMediaHandler-alphawebm-REL1_43.patch

diff --git a/includes/WebVideoTranscode/WebVideoTranscodeJob.php b/includes/WebVideoTranscode/WebVideoTranscodeJob.php
index 162be036..466f502b 100644
--- a/includes/WebVideoTranscode/WebVideoTranscodeJob.php
+++ b/includes/WebVideoTranscode/WebVideoTranscodeJob.php
@@ -19,6 +19,7 @@ use MediaWiki\Logger\LoggerFactory;
 use MediaWiki\MainConfigNames;
 use MediaWiki\Shell\CommandFactory;
 use MediaWiki\Shell\Shell;
+use MediaWiki\TimedMediaHandler\Handlers\WebMHandler\WebMHandler;
 use MediaWiki\TimedMediaHandler\HLS\Segmenter;
 use MediaWiki\TimedMediaHandler\TimedMediaHandler;
 use MediaWiki\Title\Title;
@@ -560,6 +561,24 @@ class WebVideoTranscodeJob extends Job {
 			->params( $this->config->get( MainConfigNames::ShellboxShell ), 'scripts/' . $script );
 	}
 
+	/**
+	 * Adds input codec information for more accurate input codec selection
+	 */
+	private function getInputCodec() {
+		$file = $this->getFile();
+		$handler = $file->getHandler();
+		if ( $handler instanceof WebMHandler ) {
+			$streams = $handler->getStreamTypes( $file );
+			if ( in_array( 'VP9', $streams ) ) {
+				// In order to carry out vp9 alpha channel to transcodes,
+				// it's necessary to specify the input codec as vp9,
+				// otherwise the default vp8 gets selected
+				return ' -vcodec libvpx-vp9';
+			}
+		}
+		return '';
+	}
+
 	/**
 	 * Utility helper for ffmpeg mapping
 	 * @param array $options
@@ -585,6 +604,7 @@ class WebVideoTranscodeJob extends Job {
 		$extension = substr( $transcodeKey, strrpos( $transcodeKey, '.' ) + 1 );
 
 		// Set up all the video-related options
+		$optsEnv['TMH_INPUTCODEC'] = $this->getInputCodec();
 		if ( isset( $options['novideo'] ) ) {
 			$optsEnv['TMH_OPTS_VIDEO'] = '-vn';
 		} else {
@@ -987,7 +1007,8 @@ class WebVideoTranscodeJob extends Job {
 
 		// Force to 4:2:0 chroma subsampling. Others are supported in Theora
 		// and in VP9 profile 1, but Chrome and Edge don't grok them.
-		$cmd .= ' -pix_fmt yuv420p';
+		// yuva420p allows alpha channel
+		$cmd .= ' -pix_fmt yuva420p';
 
 		// libvpx-specific constant quality or constrained quality
 		// note the range is different between VP8 and VP9
diff --git a/scripts/ffmpeg-encode.sh b/scripts/ffmpeg-encode.sh
index 94e95193..fbe53868 100644
--- a/scripts/ffmpeg-encode.sh
+++ b/scripts/ffmpeg-encode.sh
@@ -7,7 +7,7 @@ export TMH_FFMPEG_THREADS="${TMH_FFMPEG_THREADS:-2}"
 # Safe options with no user input or validated user input
 # These can be used unquoted.
 # Video related
-export TMH_FFMPEG2_OPTS TMH_MOVFLAGS TMH_OPTS_VIDEO TMH_REMUX TMH_OPT_SPEED TMH_OPT_VIDEOCODEC
+export TMH_FFMPEG2_OPTS TMH_MOVFLAGS TMH_OPTS_VIDEO TMH_REMUX TMH_OPT_SPEED TMH_OPT_VIDEOCODEC TMH_INPUTCODEC
 # Audio-related
 export TMH_OPTS_AUDIO TMH_OPT_NOAUDIO
 export TMH_OUTPUT_FILE
@@ -63,7 +63,9 @@ doFfmpegEncode() {
 
 
 	# Please note, the unquoted entries are unquoted on purpose here.
-	"$TMH_FFMPEG_PATH" -nostdin -nostats -y -i original.video \
+	"$TMH_FFMPEG_PATH" -nostdin -nostats -y \
+		$TMH_INPUTCODEC \
+		-i original.video \
 		$TMH_OPTS_VIDEO \
 		$FFMPEG2_OPTS \
 		$AUDIO_OPTS \