text: /*
   * Copyright (C) 2006 Evgeniy Stepanov <eugeni.stepanov@gmail.com>
   * Copyright (C) 2011 Grigori Goronzy <greg@chown.ath.cx>
   *
   * This file is part of libass.
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  
  #ifndef LIBASS_ASS_H
  #define LIBASS_ASS_H
  
  #include <stdio.h>
  #include <stdarg.h>
  #include "ass_types.h"
  
  #define LIBASS_VERSION 0x01400001
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /*
   * A linked list of images produced by an ass renderer.
   *
   * These images have to be rendered in-order for the correct screen
   * composition.  The libass renderer clips these bitmaps to the frame size.
   * w/h can be zero, in this case the bitmap should not be rendered at all.
   * The last bitmap row is not guaranteed to be padded up to stride size,
   * e.g. in the worst case a bitmap has the size stride * (h - 1) + w.
   */
  typedef struct ass_image {
      int w, h;                   // Bitmap width/height
      int stride;                 // Bitmap stride
      unsigned char *bitmap;      // 1bpp stride*h alpha buffer
                                  // Note: the last row may not be padded to
                                  // bitmap stride!
      uint32_t color;             // Bitmap color and alpha, RGBA
      int dst_x, dst_y;           // Bitmap placement inside the video frame
  
      struct ass_image *next;   // Next image, or NULL
  
      enum {
          IMAGE_TYPE_CHARACTER,
          IMAGE_TYPE_OUTLINE,
          IMAGE_TYPE_SHADOW
      } type;
  
      // New fields can be added here in new ABI-compatible library releases.
  } ASS_Image;
  
  /*
   * Hinting type. (see ass_set_hinting below)
   *
   * Setting hinting to anything but ASS_HINTING_NONE will put libass in a mode
   * that reduces compatibility with vsfilter and many ASS scripts. The main
   * problem is that hinting conflicts with smooth scaling, which precludes
   * animations and precise positioning.
   *
   * In other words, enabling hinting might break some scripts severely.
   *
   * FreeType's native hinter is still buggy sometimes and it is recommended
   * to use the light autohinter, ASS_HINTING_LIGHT, instead.  For best
   * compatibility with problematic fonts, disable hinting.
   */
  typedef enum {
      ASS_HINTING_NONE = 0,
      ASS_HINTING_LIGHT,
      ASS_HINTING_NORMAL,
      ASS_HINTING_NATIVE
  } ASS_Hinting;
  
  /**
   * \brief Text shaping levels.
   *
   * SIMPLE is a fast, font-agnostic shaper that can do only substitutions.
   * COMPLEX is a slower shaper using OpenType for substitutions and positioning.
   *
   * libass uses the best shaper available by default.
   */
  typedef enum {
      ASS_SHAPING_SIMPLE = 0,
      ASS_SHAPING_COMPLEX
  } ASS_ShapingLevel;
  
  /**
   * \brief Style override options. See
   * ass_set_selective_style_override_enabled() for details.
   */
  typedef enum {
      /**
       * Default mode (with no other bits set). All selective override features
       * as well as the style set with ass_set_selective_style_override() are
       * disabled, but traditional overrides like ass_set_font_scale() are
       * applied unconditionally.
       */
      ASS_OVERRIDE_DEFAULT = 0,
      /**
       * Apply the style as set with ass_set_selective_style_override() on events
       * which look like dialogue. Other style overrides are also applied this
       * way, except ass_set_font_scale(). How ass_set_font_scale() is applied
       * depends on the ASS_OVERRIDE_BIT_SELECTIVE_FONT_SCALE flag.
       *
       * This is equivalent to setting all of the following bits:
       *
       * ASS_OVERRIDE_BIT_FONT_NAME
       * ASS_OVERRIDE_BIT_FONT_SIZE_FIELDS
       * ASS_OVERRIDE_BIT_COLORS
       * ASS_OVERRIDE_BIT_BORDER
       * ASS_OVERRIDE_BIT_ATTRIBUTES
       */
      ASS_OVERRIDE_BIT_STYLE = 1 << 0,
      /**
       * Apply ass_set_font_scale() only on events which look like dialogue.
       * If not set, the font scale is applied to all events. (The behavior and
       * name of this flag are unintuitive, but exist for compatibility)
       */
      ASS_OVERRIDE_BIT_SELECTIVE_FONT_SCALE = 1 << 1,
      /**
       * Old alias for ASS_OVERRIDE_BIT_SELECTIVE_FONT_SCALE. Deprecated. Do not use.
       */
      ASS_OVERRIDE_BIT_FONT_SIZE = 1 << 1,
      /**
       * On dialogue events override: FontSize, Spacing, Blur, ScaleX, ScaleY
       */
      ASS_OVERRIDE_BIT_FONT_SIZE_FIELDS = 1 << 2,
      /**
       * On dialogue events override: FontName, treat_fontname_as_pattern
       */
      ASS_OVERRIDE_BIT_FONT_NAME = 1 << 3,
      /**
       * On dialogue events override: PrimaryColour, SecondaryColour, OutlineColour, BackColour
       */
      ASS_OVERRIDE_BIT_COLORS = 1 << 4,
      /**
       * On dialogue events override: Bold, Italic, Underline, StrikeOut
       */
      ASS_OVERRIDE_BIT_ATTRIBUTES = 1 << 5,
      /**
       * On dialogue events override: BorderStyle, Outline, Shadow
       */
      ASS_OVERRIDE_BIT_BORDER = 1 << 6,
      /**
       * On dialogue events override: Alignment
       */
      ASS_OVERRIDE_BIT_ALIGNMENT = 1 << 7,
      /**
       * On dialogue events override: MarginL, MarginR, MarginV
       */
      ASS_OVERRIDE_BIT_MARGINS = 1 << 8,
      /**
       * Unconditionally replace all fields of all styles with the one provided
       * with ass_set_selective_style_override().
       * Does not apply ASS_OVERRIDE_BIT_SELECTIVE_FONT_SCALE.
       * Add ASS_OVERRIDE_BIT_FONT_SIZE_FIELDS and ASS_OVERRIDE_BIT_BORDER if
       * you want FontSize, Spacing, Outline, Shadow to be scaled to the script
       * resolution given by the ASS_Track.
       */
      ASS_OVERRIDE_FULL_STYLE = 1 << 9,
      /**
       * On dialogue events override: Justify
       */
      ASS_OVERRIDE_BIT_JUSTIFY = 1 << 10,
      // New enum values can be added here in new ABI-compatible library releases.
  } ASS_OverrideBits;
  
  /**
   * \brief Return the version of library. This returns the value LIBASS_VERSION
   * was set to when the library was compiled.
   * \return library version
   */
  int ass_library_version(void);
  
  /**
   * \brief Default Font provider to load fonts in libass' database
   *
   * NONE don't use any default font provider for font lookup
   * AUTODETECT use the first available font provider
   * CORETEXT force a CoreText based font provider (OS X only)
   * FONTCONFIG force a Fontconfig based font provider
   *
   * libass uses the best shaper available by default.
   */
  typedef enum {
      ASS_FONTPROVIDER_NONE       = 0,
      ASS_FONTPROVIDER_AUTODETECT = 1,
      ASS_FONTPROVIDER_CORETEXT,
      ASS_FONTPROVIDER_FONTCONFIG,
      ASS_FONTPROVIDER_DIRECTWRITE,
  } ASS_DefaultFontProvider;
  
  typedef enum {
      /**
       * Enable libass extensions that would display ASS subtitles incorrectly.
       * These may be useful for applications, which use libass as renderer for
       * subtitles converted from another format, or which use libass for other
       * purposes that do not involve actual ASS subtitles authored for
       * distribution.
       */
      ASS_FEATURE_INCOMPATIBLE_EXTENSIONS,
  
      // New enum values can be added here in new ABI-compatible library releases.
  } ASS_Feature;
  
  /**
   * \brief Initialize the library.
   * \return library handle or NULL if failed
   */
  ASS_Library *ass_library_init(void);
  
  /**
   * \brief Finalize the library
   * \param priv library handle
   */
  void ass_library_done(ASS_Library *priv);
  
  /**
   * \brief Set additional fonts directory.
   * Optional directory that will be scanned for fonts recursively.  The fonts
   * found are used for font lookup.
   * NOTE: A valid font directory is not needed to support embedded fonts.
   *
   * \param priv library handle
   * \param fonts_dir directory with additional fonts
   */
  void ass_set_fonts_dir(ASS_Library *priv, const char *fonts_dir);
  
  /**
   * \brief Whether fonts should be extracted from track data.
   * \param priv library handle
   * \param extract whether to extract fonts
   */
  void ass_set_extract_fonts(ASS_Library *priv, int extract);
  
  /**
   * \brief Register style overrides with a library instance.
   * The overrides should have the form [Style.]Param=Value, e.g.
   *   SomeStyle.Font=Arial
   *   ScaledBorderAndShadow=yes
   *
   * \param priv library handle
   * \param list NULL-terminated list of strings
   */
  void ass_set_style_overrides(ASS_Library *priv, char **list);
  
  /**
   * \brief Explicitly process style overrides for a track.
   * \param track track handle
   */
  void ass_process_force_style(ASS_Track *track);
  
  /**
   * \brief Register a callback for debug/info messages.
   * If a callback is registered, it is called for every message emitted by
   * libass.  The callback receives a format string and a list of arguments,
   * to be used for the printf family of functions. Additionally, a log level
   * from 0 (FATAL errors) to 7 (verbose DEBUG) is passed.  Usually, level 5
   * should be used by applications.
   * If no callback is set, all messages level < 5 are printed to stderr,
   * prefixed with [ass].
   *
   * \param priv library handle
   * \param msg_cb pointer to callback function
   * \param data additional data, will be passed to callback
   */
  void ass_set_message_cb(ASS_Library *priv, void (*msg_cb)
                          (int level, const char *fmt, va_list args, void *data),
                          void *data);
  
  /**
   * \brief Initialize the renderer.
   * \param priv library handle
   * \return renderer handle or NULL if failed
   */
  ASS_Renderer *ass_renderer_init(ASS_Library *);
  
  /**
   * \brief Finalize the renderer.
   * \param priv renderer handle
   */
  void ass_renderer_done(ASS_Renderer *priv);
  
  /**
   * \brief Set the frame size in pixels, including margins.
   * The renderer will never return images that are outside of the frame area.
   * The value set with this function can influence the pixel aspect ratio used
   * for rendering. If the frame size doesn't equal to the video size, you may
   * have to use ass_set_pixel_aspect().
   * @see ass_set_pixel_aspect()
   * @see ass_set_margins()
   * \param priv renderer handle
   * \param w width
   * \param h height
   */
  void ass_set_frame_size(ASS_Renderer *priv, int w, int h);
  
  /**
   * \brief Set the source image size in pixels.
   * This is used to calculate the source aspect ratio and the blur scale.
   * The source image size can be reset to default by setting w and h to 0.
   * The value set with this function can influence the pixel aspect ratio used
   * for rendering.
   * @see ass_set_pixel_aspect()
   * \param priv renderer handle
   * \param w width
   * \param h height
   */
  void ass_set_storage_size(ASS_Renderer *priv, int w, int h);
  
  /**
   * \brief Set shaping level. This is merely a hint, the renderer will use
   * whatever is available if the request cannot be fulfilled.
   * \param level shaping level
   */
  void ass_set_shaper(ASS_Renderer *priv, ASS_ShapingLevel level);
  
  /**
   * \brief Set frame margins.  These values may be negative if pan-and-scan
   * is used. The margins are in pixels. Each value specifies the distance from
   * the video rectangle to the renderer frame. If a given margin value is
   * positive, there will be free space between renderer frame and video area.
   * If a given margin value is negative, the frame is inside the video, i.e.
   * the video has been cropped.
   *
   * The renderer will try to keep subtitles inside the frame area. If possible,
   * text is layout so that it is inside the cropped area. Subtitle events
   * that can't be moved are cropped against the frame area.
   *
   * ass_set_use_margins() can be used to allow libass to render subtitles into
   * the empty areas if margins are positive, i.e. the video area is smaller than
   * the frame. (Traditionally, this has been used to show subtitles in
   * the bottom "black bar" between video bottom screen border when playing 16:9
   * video on a 4:3 screen.)
   *
   * When using this function, it is recommended to calculate and set your own
   * aspect ratio with ass_set_pixel_aspect(), as the defaults won't make any
   * sense.
   * @see ass_set_pixel_aspect()
   * \param priv renderer handle
   * \param t top margin
   * \param b bottom margin
   * \param l left margin
   * \param r right margin
   */
  void ass_set_margins(ASS_Renderer *priv, int t, int b, int l, int r);
  
  /**
   * \brief Whether margins should be used for placing regular events.
   * \param priv renderer handle
   * \param use whether to use the margins
   */
  void ass_set_use_margins(ASS_Renderer *priv, int use);
  
  /**
   * \brief Set pixel aspect ratio correction.
   * This is the ratio of pixel width to pixel height.
   *
   * Generally, this is (s_w / s_h) / (d_w / d_h), where s_w and s_h is the
   * video storage size, and d_w and d_h is the video display size. (Display
   * and storage size can be different for anamorphic video, such as DVDs.)
   *
   * If the pixel aspect ratio is 0, or if the aspect ratio has never been set
   * by calling this function, libass will calculate a default pixel aspect ratio
   * out of values set with ass_set_frame_size() and ass_set_storage_size(). Note
   * that this is useful only if the frame size corresponds to the video display
   * size. Keep in mind that the margins set with ass_set_margins() are ignored
   * for aspect ratio calculations as well.
   * If the storage size has not been set, a pixel aspect ratio of 1 is assumed.
   * \param priv renderer handle
   * \param par pixel aspect ratio (1.0 means square pixels, 0 means default)
   */
  void ass_set_pixel_aspect(ASS_Renderer *priv, double par);
  
  /**
   * \brief Set aspect ratio parameters.
   * This calls ass_set_pixel_aspect(priv, dar / sar).
   * @deprecated New code should use ass_set_pixel_aspect().
   * \param priv renderer handle
   * \param dar display aspect ratio (DAR), prescaled for output PAR
   * \param sar storage aspect ratio (SAR)
   */
  void ass_set_aspect_ratio(ASS_Renderer *priv, double dar, double sar);
  
  /**
   * \brief Set a fixed font scaling factor.
   * \param priv renderer handle
   * \param font_scale scaling factor, default is 1.0
   */
  void ass_set_font_scale(ASS_Renderer *priv, double font_scale);
  
  /**
   * \brief Set font hinting method.
   * \param priv renderer handle
   * \param ht hinting method
   */
  void ass_set_hinting(ASS_Renderer *priv, ASS_Hinting ht);
  
  /**
   * \brief Set line spacing. Will not be scaled with frame size.
   * \param priv renderer handle
   * \param line_spacing line spacing in pixels
   */
  void ass_set_line_spacing(ASS_Renderer *priv, double line_spacing);
  
  /**
   * \brief Set vertical line position.
   * \param priv renderer handle
   * \param line_position vertical line position of subtitles in percent
   * (0-100: 0 = on the bottom (default), 100 = on top)
   */
  void ass_set_line_position(ASS_Renderer *priv, double line_position);
  
  /**
   * \brief Get the list of available font providers. The output array
   * is allocated with malloc and can be released with free(). If an
   * allocation error occurs, size is set to (size_t)-1.
   * \param priv library handle
   * \param providers output, list of default providers (malloc'ed array)
   * \param size output, number of providers
   * \return list of available font providers (user owns the returned array)
   */
  void ass_get_available_font_providers(ASS_Library *priv,
                                        ASS_DefaultFontProvider **providers,
                                        size_t *size);
  
  /**
   * \brief Set font lookup defaults.
   * \param default_font path to default font to use. Must be supplied if
   * fontconfig is disabled or unavailable.
   * \param default_family fallback font family for fontconfig, or NULL
   * \param dfp which font provider to use (one of ASS_DefaultFontProvider). In
   * older libass version, this could be 0 or 1, where 1 enabled fontconfig.
   * Newer relases also accept 0 (ASS_FONTPROVIDER_NONE) and 1
   * (ASS_FONTPROVIDER_AUTODETECT), which is almost backward-compatible.
   * If the requested fontprovider does not exist or fails to initialize, the
   * behavior is the same as when ASS_FONTPROVIDER_NONE was passed.
   * \param config path to fontconfig configuration file, or NULL.  Only relevant
   * if fontconfig is used.
   * \param update whether fontconfig cache should be built/updated now.  Only
   * relevant if fontconfig is used.
   *
   * NOTE: font lookup must be configured before an ASS_Renderer can be used.
   */
  void ass_set_fonts(ASS_Renderer *priv, const char *default_font,
                     const char *default_family, int dfp,
                     const char *config, int update);
  
  /**
   * \brief Set selective style override mode.
   * If enabled, the renderer attempts to override the ASS script's styling of
   * normal subtitles, without affecting explicitly positioned text. If an event
   * looks like a normal subtitle, parts of the font style are copied from the
   * user style set with ass_set_selective_style_override().
   * Warning: the heuristic used for deciding when to override the style is rather
   *          rough, and enabling this option can lead to incorrectly rendered
   *          subtitles. Since the ASS format doesn't have any support for
   *          allowing end-users to customize subtitle styling, this feature can
   *          only be implemented on "best effort" basis, and has to rely on
   *          heuristics that can easily break.
   * \param priv renderer handle
   * \param bits bit mask comprised of ASS_OverrideBits values.
   */
  void ass_set_selective_style_override_enabled(ASS_Renderer *priv, int bits);
  
  /**
   * \brief Set style for selective style override.
   * See ass_set_selective_style_override_enabled().
   * \param style style settings to use if override is enabled. Applications
   * should initialize it with {0} before setting fields. Strings will be copied
   * by the function.
   */
  void ass_set_selective_style_override(ASS_Renderer *priv, ASS_Style *style);
  
  /**
   * \brief This is a stub and does nothing. Old documentation: Update/build font
   * cache.  This needs to be called if it was disabled when ass_set_fonts was set.
   *
   * \param priv renderer handle
   * \return success
   */
  int ass_fonts_update(ASS_Renderer *priv);
  
  /**
   * \brief Set hard cache limits.  Do not set, or set to zero, for reasonable
   * defaults.
   *
   * \param priv renderer handle
   * \param glyph_max maximum number of cached glyphs
   * \param bitmap_max_size maximum bitmap cache size (in MB)
   */
  void ass_set_cache_limits(ASS_Renderer *priv, int glyph_max,
                            int bitmap_max_size);
  
  /**
   * \brief Render a frame, producing a list of ASS_Image.
   * \param priv renderer handle
   * \param track subtitle track
   * \param now video timestamp in milliseconds
   * \param detect_change compare to the previous call and set to 1
   * if positions changed, or set to 2 if content changed.
   */
  ASS_Image *ass_render_frame(ASS_Renderer *priv, ASS_Track *track,
                              long long now, int *detect_change);
  
  
  /*
   * The following functions operate on track objects and do not need
   * an ass_renderer
   */
  
  /**
   * \brief Allocate a new empty track object.
   * \param library handle
   * \return pointer to empty track
   */
  ASS_Track *ass_new_track(ASS_Library *);
  
  /**
   * \brief Enable or disable certain features
   * This manages flags that control the behavior of the renderer and how certain
   * tags etc. within the track are interpreted. The defaults on a newly created
   * ASS_Track are such that rendering is compatible with traditional renderers
   * like VSFilter, and/or old versions of libass. Calling ass_process_data() or
   * ass_process_codec_private() may change some of these flags according to file
   * headers. (ass_process_chunk() will not change any of the flags.)
   * Additions to ASS_Feature are backward compatible to old libass releases (ABI
   * compatibility).
   * \param track track
   * \param feature the specific feature to enable or disable
   * \param enable 0 for disable, any non-0 value for enable
   * \return 0 if feature set, -1 if feature is unknown
   */
  int ass_track_set_feature(ASS_Track *track, ASS_Feature feature, int enable);
  
  /**
   * \brief Deallocate track and all its child objects (styles and events).
   * \param track track to deallocate
   */
  void ass_free_track(ASS_Track *track);
  
  /**
   * \brief Allocate new style.
   * \param track track
   * \return newly allocated style id
   */
  int ass_alloc_style(ASS_Track *track);
  
  /**
   * \brief Allocate new event.
   * \param track track
   * \return newly allocated event id
   */
  int ass_alloc_event(ASS_Track *track);
  
  /**
   * \brief Delete a style.
   * \param track track
   * \param sid style id
   * Deallocates style data. Does not modify track->n_styles.
   */
  void ass_free_style(ASS_Track *track, int sid);
  
  /**
   * \brief Delete an event.
   * \param track track
   * \param eid event id
   * Deallocates event data. Does not modify track->n_events.
   */
  void ass_free_event(ASS_Track *track, int eid);
  
  /**
   * \brief Parse a chunk of subtitle stream data.
   * \param track track
   * \param data string to parse
   * \param size length of data
   */
  void ass_process_data(ASS_Track *track, char *data, int size);
  
  /**
   * \brief Parse Codec Private section of the subtitle stream, in Matroska
   * format.  See the Matroska specification for details.
   * \param track target track
   * \param data string to parse
   * \param size length of data
   */
  void ass_process_codec_private(ASS_Track *track, char *data, int size);
  
  /**
   * \brief Parse a chunk of subtitle stream data. A chunk contains exactly one
   * event in Matroska format.  See the Matroska specification for details.
   * In later libass versions (since LIBASS_VERSION==0x01300001), using this
   * function means you agree not to modify events manually, or using other
   * functions manipulating the event list like ass_process_data(). If you do
   * anyway, the internal duplicate checking might break. Calling
   * ass_flush_events() is still allowed.
   * \param track track
   * \param data string to parse
   * \param size length of data
   * \param timecode starting time of the event (milliseconds)
   * \param duration duration of the event (milliseconds)
   */
  void ass_process_chunk(ASS_Track *track, char *data, int size,
                         long long timecode, long long duration);
  
  /**
   * \brief Set whether the ReadOrder field when processing a packet with
   * ass_process_chunk() should be used for eliminating duplicates.
   * \param check_readorder 0 means do not try to eliminate duplicates; 1 means
   * use the ReadOrder field embedded in the packet as unique identifier, and
   * discard the packet if there was already a packet with the same ReadOrder.
   * Other values are undefined.
   * If this function is not called, the default value is 1.
   */
  void ass_set_check_readorder(ASS_Track *track, int check_readorder);
  
  /**
   * \brief Flush buffered events.
   * \param track track
  */
  void ass_flush_events(ASS_Track *track);
  
  /**
   * \brief Read subtitles from file.
   * \param library library handle
   * \param fname file name
   * \param codepage encoding (iconv format)
   * \return newly allocated track
  */
  ASS_Track *ass_read_file(ASS_Library *library, char *fname,
                           char *codepage);
  
  /**
   * \brief Read subtitles from memory.
   * \param library library handle
   * \param buf pointer to subtitles text
   * \param bufsize size of buffer
   * \param codepage encoding (iconv format)
   * \return newly allocated track
  */
  ASS_Track *ass_read_memory(ASS_Library *library, char *buf,
                             size_t bufsize, char *codepage);
  /**
   * \brief Read styles from file into already initialized track.
   * \param fname file name
   * \param codepage encoding (iconv format)
   * \return 0 on success
   */
  int ass_read_styles(ASS_Track *track, char *fname, char *codepage);
  
  /**
   * \brief Add a memory font.
   * \param library library handle
   * \param name attachment name
   * \param data binary font data
   * \param data_size data size
  */
  void ass_add_font(ASS_Library *library, char *name, char *data,
                    int data_size);
  
  /**
   * \brief Remove all fonts stored in an ass_library object.
   * \param library library handle
   */
  void ass_clear_fonts(ASS_Library *library);
  
  /**
   * \brief Calculates timeshift from now to the start of some other subtitle
   * event, depending on movement parameter.
   * \param track subtitle track
   * \param now current time in milliseconds
   * \param movement how many events to skip from the one currently displayed
   * +2 means "the one after the next", -1 means "previous"
   * \return timeshift in milliseconds
   */
  long long ass_step_sub(ASS_Track *track, long long now, int movement);
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif /* LIBASS_ASS_H */
  