Add additional format options for transparency

Updated ProRes to allow transparent output when set to Profile 4. As
part of this change, pix_fmt is no longer explicitly set for ProRes, but
the expected format is automatically applied from for each profile.

Added rgba as an output pix_fmt for the nvenc formats. These have not
been tested and may not function.

Fix incorrect escape in Advanced Preview code.

video_formats/ProRes.json

@@ -2,8 +2,7 @@
     "main_pass":
     [
         "-n", "-c:v", "prores_ks",
-        "-profile:v","3",
-        "-pix_fmt", "yuv422p10"
+        "-profile:v", ["profile",["1","2","3","4"], {"default": "3"}]
     ],
     "audio_pass": ["-c:a", "pcm_s16le"],
     "extension": "mov"

video_formats/nvenc_h264-mp4.json

@@ -2,7 +2,7 @@
     "main_pass":
     [
         "-n", "-c:v", "h264_nvenc",
-        "-pix_fmt", ["pix_fmt", ["yuv420p", "yuv420p10le"]]
+        "-pix_fmt", ["pix_fmt", ["yuv420p", "yuv420p10le", "rgba"]]
     ],
     "audio_pass": ["-c:a", "aac"],
     "bitrate": ["bitrate","INT", {"default": 10, "min": 1, "max": 999, "step": 1 }],

video_formats/nvenc_hevc-mp4.json

@@ -3,7 +3,7 @@
     [
         "-n", "-c:v", "hevc_nvenc",
         "-vtag", "hvc1",
-        "-pix_fmt", ["pix_fmt", ["yuv420p", "yuv420p10le"]]
+        "-pix_fmt", ["pix_fmt", ["yuv420p", "yuv420p10le", "rgba"]]
     ],
     "audio_pass": ["-c:a", "aac"],
     "bitrate": ["bitrate","INT", {"default": 10, "min": 1, "max": 999, "step": 1 }],

videohelpersuite/server.py

@@ -77,7 +77,7 @@ async def view_video(request):
     try:
         res = subprocess.run(['ffmpeg'] + in_args + ['-t', '0', '-f', 'null', '-'],
                              capture_output=True, check=True)
-        match = re.search(': Video: (\\w+) .+, (\d+) fps,', res.stderr.decode('utf-8'))
+        match = re.search(': Video: (\\w+) .+, (\\d+) fps,', res.stderr.decode('utf-8'))
         if match:
             base_fps = float(match.group(2))
             if match.group(1) == 'vp9':