doc: Grammar fixes for FFmpeg description

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

doc/ffmpeg.texi

@@ -16,26 +16,26 @@ ffmpeg [@var{global_options}] @{[@var{input_file_options}] -i @file{input_file}@
 @chapter Description
 @c man begin DESCRIPTION
 
-ffmpeg is a very fast video and audio converter that can also grab from
+@command{ffmpeg} is a very fast video and audio converter that can also grab from
 a live audio/video source. It can also convert between arbitrary sample
 rates and resize video on the fly with a high quality polyphase filter.
 
-ffmpeg reads from an arbitrary number of input "files" (which can be regular
+@command{ffmpeg} reads from an arbitrary number of input "files" (which can be regular
 files, pipes, network streams, grabbing devices, etc.), specified by the
 @code{-i} option, and writes to an arbitrary number of output "files", which are
 specified by a plain output filename. Anything found on the command line which
 cannot be interpreted as an option is considered to be an output filename.
 
-Each input or output file can in principle contain any number of streams of
-different types (video/audio/subtitle/attachment/data). Allowed number and/or
-types of streams can be limited by the container format. Selecting, which
-streams from which inputs go into output, is done either automatically or with
-the @code{-map} option (see the Stream selection chapter).
+Each input or output file can, in principle, contain any number of streams of
+different types (video/audio/subtitle/attachment/data). The allowed number and/or
+types of streams may be limited by the container format. Selecting which
+streams from which inputs will go into which output is either done automatically
+or with the @code{-map} option (see the Stream selection chapter).
 
 To refer to input files in options, you must use their indices (0-based). E.g.
-the first input file is @code{0}, the second is @code{1} etc. Similarly, streams
+the first input file is @code{0}, the second is @code{1}, etc. Similarly, streams
 within a file are referred to by their indices. E.g. @code{2:3} refers to the
-fourth stream in the third input file. See also the Stream specifiers chapter.
+fourth stream in the third input file. Also see the Stream specifiers chapter.
 
 As a general rule, options are applied to the next specified
 file. Therefore, order is important, and you can have the same
@@ -50,7 +50,7 @@ options apply ONLY to the next input or output file and are reset between files.
 
 @itemize
 @item
-To set the video bitrate of the output file to 64kbit/s:
+To set the video bitrate of the output file to 64 kbit/s:
 @example
 ffmpeg -i input.avi -b:v 64k -bufsize 64k output.avi
 @end example