Update defaults and docs for video attributes

Closes #1679.

telethon/client/uploads.py

@@ -201,9 +201,14 @@ async def send_file(
                 Optional JPEG thumbnail (for documents). **Telegram will
                 ignore this parameter** unless you pass a ``.jpg`` file!
 
-                The file must also be small in dimensions and in-disk size.
-                Successful thumbnails were files below 20kb and 200x200px.
+                The file must also be small in dimensions and in disk size.
+                Successful thumbnails were files below 20kB and 320x320px.
                 Width/height and dimensions/size ratios may be important.
+                For Telegram to accept a thumbnail, you must provide the
+                dimensions of the underlying media through ``attributes=``
+                with :tl:`DocumentAttributesVideo` or by installing the
+                optional ``hachoir`` dependency.
+
 
             allow_cache (`bool`, optional):
                 This parameter currently does nothing, but is kept for

telethon/utils.py

@@ -694,10 +694,10 @@ def get_attributes(file, *, attributes=None, mime_type=None,
         if m:
             doc = types.DocumentAttributeVideo(
                 round_message=video_note,
-                w=m.get('width') if m.has('width') else 0,
-                h=m.get('height') if m.has('height') else 0,
+                w=m.get('width') if m.has('width') else 1,
+                h=m.get('height') if m.has('height') else 1,
                 duration=int(m.get('duration').seconds
-                             if m.has('duration') else 0),
+                             if m.has('duration') else 1),
                 supports_streaming=supports_streaming
             )
         elif thumb:
@@ -708,7 +708,7 @@ def get_attributes(file, *, attributes=None, mime_type=None,
                 width = t_m.get("width")
             if t_m and t_m.has("height"):
                 height = t_m.get("height")
-            
+
             doc = types.DocumentAttributeVideo(
                 0, width, height, round_message=video_note,
                 supports_streaming=supports_streaming)