Update playing videos

Remove note about not being able to seek Theora files. Add information
about encoding files with FFmpeg.

Author: berarma

tutorials/animation/playing_videos.rst

@@ -8,9 +8,10 @@ Godot supports video playback with the :ref:`class_VideoStreamPlayer` node.
 Supported playback formats
 --------------------------
 
-The only supported format in core is **Ogg Theora** (not to be confused with Ogg
-Vorbis audio). It's possible for extensions to bring support for additional
-formats, but no such extensions exist yet as of July 2022.
+The only supported format in core is **Ogg Theora** (not to be confused with
+Ogg Vorbis audio) with optional Ogg Vorbis audio tracks. It's possible for
+extensions to bring support for additional formats, but no such extensions
+exist yet as of July 2022.
 
 H.264 and H.265 cannot be supported in core Godot, as they are both encumbered
 by software patents. AV1 is royalty-free, but it remains slow to decode on the
@@ -152,7 +153,6 @@ Playback limitations
 
 There are several limitations with the current implementation of video playback in Godot:
 
-- Seeking a video to a certain point is not supported.
 - Changing playback speed is not supported. VideoStreamPlayer also won't follow
   :ref:`Engine.time_scale<class_Engine_property_time_scale>`.
 - Streaming a video from a URL is not supported.
@@ -195,6 +195,12 @@ below with almost any input video format (AVI, MOV, WebM, …).
    You can check this by running ``ffmpeg`` without any arguments, then looking
    at the ``configuration:`` line in the command output.
 
+.. warning::
+
+   FFmpeg will erroneuosly drop identical frames when performing a copy of a
+   Theora stream producing an incorrect video file. Avoid it by always
+   transcoding video.
+
 Balancing quality and file size
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -217,6 +223,19 @@ dropouts in case of high system load. See
 for a table listing Ogg Vorbis audio quality presets and their respective
 variable bitrates.
 
+The **GOP size** (``-g:v``) can provide further compression by increasing the
+interval between keyframes. The defaul value is pretty low (12). Higher values
+can provide better compression at the expense of some quality and slightly
+slower seeks. Increasing GOP size usually produces better results than reducing
+video quality and it's thus recommended.
+
+.. note::
+
+   GOP sizes above 64 will cause seeks to be slower, more noticeably beyond
+   every power of two. Also, due to some supposed bug in FFmpeg, using a GOP
+   size greater than 64 can slow down seeking even more and might create bigger
+   files.
+
 FFmpeg: Convert while preserving original video resolution
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -227,7 +246,7 @@ static scenes).
 
 ::
 
-    ffmpeg -i input.mp4 -q:v 6 -q:a 6 output.ogv
+    ffmpeg -i input.mp4 -q:v 6 -g:v 30 -q:a 6 output.ogv
 
 FFmpeg: Resize the video then convert it
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -238,7 +257,7 @@ significantly if the source is recorded at a higher resolution than 720p:
 
 ::
 
-    ffmpeg -i input.mp4 -vf "scale=-1:720" -q:v 6 -q:a 6 output.ogv
+    ffmpeg -i input.mp4 -vf "scale=-1:720" -q:v 6 -g:v 30 -q:a 6 output.ogv
 
 
 .. Chroma Key Functionality Documentation