GH-29: Fix the image compression option (GH-57)

* Change the frame size calculation
* Optimize the calculation of columns' count
* Limit the final image size be at most 8K
* Allow `0` as a value for the `--compress` option
* Update snapshots for related test cases

Author: ArtyomVancyan

src/thumbnails/__init__.py

@@ -22,7 +22,7 @@
 from .thumbnail import ThumbnailVTT
 from .thumbnail import register_thumbnail
 
-__version__ = "0.1.4"
+__version__ = "0.1.5"
 __all__ = (
     "Generator",
     "Thumbnail",

src/thumbnails/frame.py

@@ -5,33 +5,50 @@ class _Frame:
     """This class is used to calculate the optimal size of a thumbnail frame."""
 
     def __init__(self, size):
-        width, height = size
-        _min_width = 300
-        _min_height = math.ceil(_min_width * height / width)
+        # Original size of the frame
+        self._width, self._height = size
 
+        # Minimum size of the frame
+        self._min_width = 30
+        self._min_height = math.ceil(self._min_width * self._height / self._width)
+
+        # Maximum size of the frame
+        self._max_width = 7680 // self.columns_count  # 7680 is the width of 8K
+        self._max_height = math.ceil(self._max_width * self._height / self._width)
+
+        # Final size of the frame
         self.__width = None
         self.__height = None
 
-        self._width = width / 10
-        self._height = height / 10
-        self._min_width = _min_width
-        self._min_height = _min_height
-
     @property
     def compress(self):
         """Defines an interface for the compress property."""
         raise NotImplementedError
 
+    @property
+    def frames_count(self):
+        """Defines an interface for the frames_count property."""
+        raise NotImplementedError
+
+    @property
+    def columns_count(self):
+        """Defines an interface for the columns_count property."""
+        raise NotImplementedError
+
     @property
     def width(self):
         """Calculates and caches the frame width."""
         if not self.__width:
-            self.__width = max(self._min_width, self._width * self.compress)
+            self.__width = round(self._width * self.compress)
+            self.__width = max(self.__width, self._min_width)
+            self.__width = min(self.__width, self._max_width)
         return self.__width
 
     @property
     def height(self):
         """Calculates and caches the frame height."""
         if not self.__height:
-            self.__height = max(self._min_height, self._height * self.compress)
+            self.__height = round(self._height * self.compress)
+            self.__height = max(self.__height, self._min_height)
+            self.__height = min(self.__height, self._max_height)
         return self.__height

src/thumbnails/video.py

@@ -34,10 +34,12 @@ def __init__(self, filepath, compress, interval):
         self.__compress = float(compress)
         self.__interval = float(interval)
 
-        if self.__compress <= 0 or self.__compress > 1:
+        if self.__compress < 0 or self.__compress > 1:
             raise ValueError("Compress must be between 0 and 1.")
 
         self.tempdir = TemporaryDirectory()
+        self.__frames_count = None
+        self.__columns = None
 
         _FFMpeg.__init__(self, filepath)
         _Frame.__init__(self, self.size)
@@ -54,12 +56,26 @@ def compress(self):
     def interval(self):
         return self.__interval
 
-    @staticmethod
-    def calc_columns(frames_count, width, height):
+    @property
+    def frames_count(self):
+        """Calculates and caches the count of frames."""
+        if not self.__frames_count:
+            self.__frames_count = len(arange(0, self.duration, self.interval))
+        return self.__frames_count
+
+    @property
+    def columns_count(self):
+        """Calculates and caches the count of columns."""
+        if not self.__columns:
+            self.__columns = self.calc_columns()
+        return self.__columns
+
+    def calc_columns(self):
         """Calculates an optimal number of columns for 16:9 aspect ratio."""
         ratio = 16 / 9
-        for col in range(1, frames_count):
-            if (col * width) / (frames_count // col * height) > ratio:
+        width, height = self.size
+        for col in range(1, self.frames_count):
+            if (col * width) / (self.frames_count // col * height) > ratio:
                 return col
 
     def _extract_frame(self, start_time):
@@ -102,11 +118,12 @@ def thumbnails(self, master_size=False):
         """
         line, column = 0, 0
         frames = sorted(glob.glob(self.tempdir.name + os.sep + "*.png"))
-        frames_count = len(arange(0, self.duration, self.interval))
-        columns = self.calc_columns(frames_count, self.width, self.height)
 
         if master_size:
-            yield self.width * columns, self.height * math.ceil(frames_count / columns)
+            yield (
+                self.width * self.columns_count,
+                self.height * math.ceil(self.frames_count / self.columns_count)
+            )
 
         for n, frame in enumerate(frames):
             x, y = self.width * column, self.height * line
@@ -117,6 +134,6 @@ def thumbnails(self, master_size=False):
 
             column += 1
 
-            if column == columns:
+            if column == self.columns_count:
                 line += 1
                 column = 0

tests/data/snapshots/relative-base-json

@@ -1,46 +1,46 @@
 {
   "0": {
     "src": "%(tmp_media)s/video/0-00-00.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "10": {
     "src": "%(tmp_media)s/video/0-00-10.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "20": {
     "src": "%(tmp_media)s/video/0-00-20.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "30": {
     "src": "%(tmp_media)s/video/0-00-30.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "40": {
     "src": "%(tmp_media)s/video/0-00-40.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "50": {
     "src": "%(tmp_media)s/video/0-00-50.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "60": {
     "src": "%(tmp_media)s/video/0-01-00.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "70": {
     "src": "%(tmp_media)s/video/0-01-10.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "80": {
     "src": "%(tmp_media)s/video/0-01-20.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "90": {
     "src": "%(tmp_media)s/video/0-01-30.png",
-    "width": "300px"
+    "width": "2560px"
   },
   "100": {
     "src": "%(tmp_media)s/video/0-01-40.png",
-    "width": "300px"
+    "width": "2560px"
   }
 }

tests/data/snapshots/relative-base-vtt

@@ -1,35 +1,35 @@
 WEBVTT
 
 00:00:00.000 --> 00:00:10.000
-%(tmp_media)s/video.png#xywh=0,0,300,126
+%(tmp_media)s/video.png#xywh=0,0,2560,1072
 
 00:00:10.000 --> 00:00:20.000
-%(tmp_media)s/video.png#xywh=300,0,300,126
+%(tmp_media)s/video.png#xywh=2560,0,2560,1072
 
 00:00:20.000 --> 00:00:30.000
-%(tmp_media)s/video.png#xywh=600,0,300,126
+%(tmp_media)s/video.png#xywh=5120,0,2560,1072
 
 00:00:30.000 --> 00:00:40.000
-%(tmp_media)s/video.png#xywh=0,126,300,126
+%(tmp_media)s/video.png#xywh=0,1072,2560,1072
 
 00:00:40.000 --> 00:00:50.000
-%(tmp_media)s/video.png#xywh=300,126,300,126
+%(tmp_media)s/video.png#xywh=2560,1072,2560,1072
 
 00:00:50.000 --> 00:01:00.000
-%(tmp_media)s/video.png#xywh=600,126,300,126
+%(tmp_media)s/video.png#xywh=5120,1072,2560,1072
 
 00:01:00.000 --> 00:01:10.000
-%(tmp_media)s/video.png#xywh=0,252,300,126
+%(tmp_media)s/video.png#xywh=0,2144,2560,1072
 
 00:01:10.000 --> 00:01:20.000
-%(tmp_media)s/video.png#xywh=300,252,300,126
+%(tmp_media)s/video.png#xywh=2560,2144,2560,1072
 
 00:01:20.000 --> 00:01:30.000
-%(tmp_media)s/video.png#xywh=600,252,300,126
+%(tmp_media)s/video.png#xywh=5120,2144,2560,1072
 
 00:01:30.000 --> 00:01:40.000
-%(tmp_media)s/video.png#xywh=0,378,300,126
+%(tmp_media)s/video.png#xywh=0,3216,2560,1072
 
 00:01:40.000 --> 00:01:50.000
-%(tmp_media)s/video.png#xywh=300,378,300,126
+%(tmp_media)s/video.png#xywh=2560,3216,2560,1072
 

tests/data/snapshots/specified-base-json

@@ -1,46 +1,46 @@
 {
   "0": {
     "src": "/media/thumbnails/video/0-00-00.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "10": {
     "src": "/media/thumbnails/video/0-00-10.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "20": {
     "src": "/media/thumbnails/video/0-00-20.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "30": {
     "src": "/media/thumbnails/video/0-00-30.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "40": {
     "src": "/media/thumbnails/video/0-00-40.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "50": {
     "src": "/media/thumbnails/video/0-00-50.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "60": {
     "src": "/media/thumbnails/video/0-01-00.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "70": {
     "src": "/media/thumbnails/video/0-01-10.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "80": {
     "src": "/media/thumbnails/video/0-01-20.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "90": {
     "src": "/media/thumbnails/video/0-01-30.png",
-    "width": "300px"
+    "width": "1280px"
   },
   "100": {
     "src": "/media/thumbnails/video/0-01-40.png",
-    "width": "300px"
+    "width": "1280px"
   }
 }

tests/data/snapshots/specified-base-vtt

@@ -1,35 +1,35 @@
 WEBVTT
 
 00:00:00.000 --> 00:00:10.000
-/media/thumbnails/video.png#xywh=0,0,300,126
+/media/thumbnails/video.png#xywh=0,0,1280,536
 
 00:00:10.000 --> 00:00:20.000
-/media/thumbnails/video.png#xywh=300,0,300,126
+/media/thumbnails/video.png#xywh=1280,0,1280,536
 
 00:00:20.000 --> 00:00:30.000
-/media/thumbnails/video.png#xywh=600,0,300,126
+/media/thumbnails/video.png#xywh=2560,0,1280,536
 
 00:00:30.000 --> 00:00:40.000
-/media/thumbnails/video.png#xywh=0,126,300,126
+/media/thumbnails/video.png#xywh=0,536,1280,536
 
 00:00:40.000 --> 00:00:50.000
-/media/thumbnails/video.png#xywh=300,126,300,126
+/media/thumbnails/video.png#xywh=1280,536,1280,536
 
 00:00:50.000 --> 00:01:00.000
-/media/thumbnails/video.png#xywh=600,126,300,126
+/media/thumbnails/video.png#xywh=2560,536,1280,536
 
 00:01:00.000 --> 00:01:10.000
-/media/thumbnails/video.png#xywh=0,252,300,126
+/media/thumbnails/video.png#xywh=0,1072,1280,536
 
 00:01:10.000 --> 00:01:20.000
-/media/thumbnails/video.png#xywh=300,252,300,126
+/media/thumbnails/video.png#xywh=1280,1072,1280,536
 
 00:01:20.000 --> 00:01:30.000
-/media/thumbnails/video.png#xywh=600,252,300,126
+/media/thumbnails/video.png#xywh=2560,1072,1280,536
 
 00:01:30.000 --> 00:01:40.000
-/media/thumbnails/video.png#xywh=0,378,300,126
+/media/thumbnails/video.png#xywh=0,1608,1280,536
 
 00:01:40.000 --> 00:01:50.000
-/media/thumbnails/video.png#xywh=300,378,300,126
+/media/thumbnails/video.png#xywh=1280,1608,1280,536