在nginx中使用变量hls_path

Question

现在我将hls创建的所有文件和文件夹保存在一个目录中，如

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application live {
                    live on; # Allows live input

                    # Once receive stream, transcode for adaptive streaming
                    # This single ffmpeg command takes the input and transforms
                    # the source into 4 different streams with different bitrate
                    # and quality. P.S. The scaling done here respects the aspect
                    # ratio of the input.
                    exec ffmpeg -i rtmp://127.0.0.1/$app/$name -async 1 -vsync -1
                            -c:v libx264 -c:a aac -strict -2 -b:v 256k -b:a 32k -vf "scale=480:trunc(ow/a/2)*2" -tune zerolatency -preset veryfast$
                            -c:v libx264 -c:a aac -strict -2 -b:v 768k -b:a 96k -vf "scale=720:trunc(ow/a/2)*2" -tune zerolatency -preset veryfast$
                            -c:v libx264 -c:a aac -strict -2 -b:v 1024k -b:a 128k -vf "scale=960:trunc(ow/a/2)*2" -tune zerolatency -preset veryfa$
                            -c:v libx264 -c:a aac -strict -2 -b:v 1920k -b:a 128k -vf "scale=1280:trunc(ow/a/2)*2" -tune zerolatency -preset veryf$
                            -c copy -f flv rtmp://127.0.0.1/show/$name_src;
            }

            # This application is for splitting the stream into HLS fragments
            application show {
                    live on; # Allows live input from above
                    hls on; # Enable HTTP Live Streaming
                    hls_cleanup off;
                    hls_nested on;

                    # Pointing this to an SSD is better as this involves lots of IO
                    #exec mkdir /mnt/HLS/;
                    hls_path /mnt/HLS/;

                    # Instruct clients to adjust resolution according to bandwidth
                    hls_variant _low BANDWIDTH=288000; # Low bitrate, sub-SD resolution
                    hls_variant _mid BANDWIDTH=448000; # Medium bitrate, SD resolution
                    hls_variant _high BANDWIDTH=1152000; # High bitrate, higher-than-SD resolution
                    hls_variant _hd720 BANDWIDTH=2048000; # High bitrate, HD 720p resolution

}

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如何根据流的名称为每个hls流创建一个新目录。