avs_defns.h

/*
 * Datastructures for reading AVS elementary streams.
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is the MPEG TS, PS and ES tools.
 *
 * The Initial Developer of the Original Code is Amino Communications Ltd.
 * Portions created by the Initial Developer are Copyright (C) 2008
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Amino Communications Ltd, Swavesey, Cambridge UK
 *
 * ***** END LICENSE BLOCK *****
 */

#ifndef _avs_defns
#define _avs_defns

#include <stdio.h>
#include "compat.h"
#include "es_defns.h"
#include "ts_defns.h"

// Since reverse_data refers to avs and acces_unit datastructures, and
// *they* refer to reverse_data, we need to break the circular referencing
// at some point
typedef struct avs_context *avs_context_p;
#include "reverse_defns.h"

// ------------------------------------------------------------
// An AVS frame. This might be a picture or a sequence header (and
// its associated ES units).
struct _avs_frame
{
  // The main thing we need is a list of the units that make up this picture
  ES_unit_list_p    list;

  // An AVS "picture" might be a "proper" picture, a sequence header,
  // or (just) a sequence end item. It's useful to be able to identify
  // the two more common cases easily
  int       is_frame;
  int       is_sequence_header;

  // It's also useful to remember what the first ES unit is
  int       start_code;

  // Data defined for a frame.
  byte      picture_coding_type;  // I, P or B (0, 1, 2)
  byte      picture_distance;     // presentation order of P/B frames

  // Data defined for a sequence header
  byte      aspect_ratio;         // 1=SAR/1.0 2=4/3, 3=16/9, 4=2.21/1 (?)
  byte      frame_rate_code;      // see Table 7-6
};
typedef struct _avs_frame *avs_frame_p;
#define SIZEOF_AVS_FRAME sizeof(struct _avs_frame)

// ------------------------------------------------------------
#define is_avs_slice_item(unit)           ((unit)->start_code<0xB0)
#define is_avs_frame_item(unit)           ((unit)->start_code==0xB3 || \
                                           (unit)->start_code==0xB6)
#define is_avs_user_data_item(unit)       ((unit)->start_code==0xB2)
#define is_avs_seq_header_item(unit)      ((unit)->start_code==0xB0)
#define is_avs_seq_end_item(unit)         ((unit)->start_code==0xB1)
#define is_avs_extension_start_item(unit) ((unit)->start_code==0xB5)
#define is_avs_video_edit_item(unit)      ((unit)->start_code==0xB7)

#define avs_frame_rate(code)    ((code)==1?24000.0/1001: /* 23.967... */\
                                 (code)==2?24:                          \
                                 (code)==3?25:                          \
                                 (code)==4?30000.0/1001: /* 29.97... */ \
                                 (code)==5?30:                          \
                                 (code)==6?50:                          \
                                 (code)==7?60000.0/1001: /* 59.94... */ \
                                 (code)==8?60:                          \
                                 25)                     /* Hmm-really an error */

#define AVS_I_PICTURE_CODING    0 // our invention, but reasonable in context
#define AVS_P_PICTURE_CODING    1
#define AVS_B_PICTURE_CODING    2

// Note that "I" is made up by us (there is no picture coding on I frames)
#define AVS_PICTURE_CODING_STR(s)  \
  ((s)==AVS_I_PICTURE_CODING?"I":  \
   (s)==AVS_P_PICTURE_CODING?"P":  \
   (s)==AVS_B_PICTURE_CODING?"B":  \
   "Reserved")

// ------------------------------------------------------------
// Context for looping over the AVS items and pictures in an elementary
// stream
struct avs_context
{
  ES_p           es;

  // We count all of the frames as we read them (this is useful
  // when we are building up reverse_data arrays). If functions
  // move around in the data stream, we assume that they will
  // (re)set this to a sensible value.
  // The index of the first frame read is 1, and this value is
  // incremented by each call of `get_next_avs_frame` (note that
  // for this purpose, sequence headers are *not* considered frames)
  uint32_t       frame_index;  // The index of the last frame read
  
  // We detect the end of an AVS frame (or sequence header) by
  // reading the first item that cannot be part of it. We then need
  // to remember that item for *next* time we try to read a frame.
  ES_unit_p    last_item;
  
  // If we are collecting reversing information, then we keep a reference
  // to the reverse data here
  reverse_data_p reverse_data;
  // In the same context, we need to remember how long it is since the
  // last sequence header
  byte           count_since_seq_hdr;
};
#define SIZEOF_AVS_CONTEXT sizeof(struct avs_context)

#endif // _avs_defns

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