lavf/img2doc: document options

doc/demuxers.texi

@@ -34,8 +34,9 @@ specified in the pattern with the string "%%".
 
 If the pattern contains "%d" or "%0@var{N}d", the first filename of
 the file list specified by the pattern must contain a number
-inclusively contained between 0 and 4, all the following numbers must
-be sequential. This limitation may be hopefully fixed.
+inclusively contained between @var{start_number} and
+@var{start_number}+4, all the following numbers must be
+sequential.
 
 The pattern may contain a suffix which is used to automatically
 determine the format of the images contained in the files.
@@ -49,6 +50,23 @@ sequence of filenames of the form @file{i%m%g-1.jpg},
 The size, the pixel format, and the format of each image must be the
 same for all the files in the sequence.
 
+This demuxer accepts the following options:
+@table @option
+@item framerate
+Set the framerate for the video stream. It defaults to 25.
+@item loop
+If set to 1, loop over the input. Default value is 0.
+@item pixel_format
+Set the pixel format of the images to read. If not specified the pixel
+format is guessed from the first image file in the sequence.
+@item start_number
+Set the index of the file matched by the image file pattern to start
+to read from. Default value is 0.
+@item video_size
+Set the video size of the images to read. If not specified the video
+size is guessed from the first image file in the sequence.
+@end table
+
 The following example shows how to use @command{ffmpeg} for creating a
 video from the images in the file sequence @file{img-001.jpeg},
 @file{img-002.jpeg}, ..., assuming an input frame rate of 10 frames per
@@ -57,6 +75,11 @@ second:
 ffmpeg -i 'img-%03d.jpeg' -r 10 out.mkv
 @end example
 
+As above, but start by reading from a file with index 100 in the sequence:
+@example
+ffmpeg -start_number 100 -i 'img-%03d.jpeg' -r 10 out.mkv
+@end example
+
 Note that the pattern must not necessarily contain "%d" or
 "%0@var{N}d", for example to convert a single image file
 @file{img.jpeg} you can employ the command: