Merge pull request #262632 from sally-baolian/patch-187

Update batch-synthesis-avatar-properties.md

Author: prmerger-automator[bot]

articles/ai-services/speech-service/text-to-speech-avatar/batch-synthesis-avatar-properties.md

@@ -29,7 +29,7 @@ The following table describes the avatar properties.
 | properties.talkingAvatarStyle             | The style name of the talking avatar.<br/><br/>The supported avatar styles can be found [here](avatar-gestures-with-ssml.md#supported-pre-built-avatar-characters-styles-and-gestures).<br/><br/>This property is required for prebuilt avatar, and optional for customized avatar.|
 | properties.customized                     | A bool value indicating whether the avatar to be used is customized avatar or not. True for customized avatar, and false for prebuilt avatar.<br/><br/>This property is optional, and the default value is `false`.|
 | properties.videoFormat                    | The format for output video file, could be mp4 or webm.<br/><br/>The `webm` format is required for transparent background.<br/><br/>This property is optional, and the default value is mp4.|
-| properties.videoCodec                     | The codec for output video, could be h264, hevc or vp9.<br/><br/>Vp9 is required for transparent background.<br/><br/>This property is optional, and the default value is hevc.|
+| properties.videoCodec                     | The codec for output video, could be h264, hevc or vp9.<br/><br/>Vp9 is required for transparent background. The synthesis speed will be slower with vp9 codec, as vp9 encoding is slower.<br/><br/>This property is optional, and the default value is hevc.|
 | properties.kBitrate (bitrateKbps)          | The bitrate for output video, which is integer value, with unit kbps.<br/><br/>This property is optional, and the default value is 2000.|
 | properties.videoCrop                      | This property allows you to crop the video output, which means, to output a rectangle subarea of the original video. This property has two fields, which define the top-left vertex and bottom-right vertex of the rectangle.<br/><br/>This property is optional, and the default behavior is to output the full video.|
 | properties.videoCrop.topLeft              |The top-left vertex of the rectangle for video crop. This property has two fields x and y, to define the horizontal and vertical position of the vertex.<br/><br/>This property is required when properties.videoCrop is set.|