filter_defns.h

/*
 * Datastructures for filtering ES data ("fast forward") and writing to ES or
 * TS.
 *
 * ***** 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 _filter_defns
#define _filter_defns

#include "compat.h"
#include "es_defns.h"
#include "h262_defns.h"
#include "accessunit_defns.h"
#include "reverse_defns.h"

// Filtering comes in two varieties:
// - "stripping" means retaining just reference pictures. For H.262 this
//   means the I pictures (and maybe the P pictures), for H.264 this means
//   the IDR and I pictures (or maybe all reference pictures). This is simple
//   to do, but the speedup resulting is very dependant on the data.
// - "filtering" means attempting to keep frames as a particular frequency,
//   so, for instance, a frequency of 8 would mean trying to keep every 8th
//   frame, or a speedup of 8x. This is harder to do as it depends rather
//   crucially on the distribution of reference frames in the data.

// ------------------------------------------------------------
struct h262_filter_context
{
  h262_context_p  h262; // The H.262 stream we are reading from
  int   filter;  // TRUE if filtering, FALSE if stripping
  int   freq;    // Frequency of frames to try to keep if filtering
  int   allref;  // Keep all I and P pictures if stripping?
  // (the name `allref` is used for compatibility with the H.264 filter
  // context - it's a little easier to have one name for both filters)

  // For any operation on H.262, we want:
  int   pending_EOF;  // next time a function is called, say we had EOF

  // When filtering, we want:
  int   count;    // a rolling count to compare with the desired frequency
  int   last_was_slice;
  int   had_previous_picture;
  h262_picture_p  last_seq_hdr;

  // When stripping, we want:
  int   new_seq_hdr;    // has the sequence header changed?

  int   frames_seen;    // number of pictures seen this filter run
  int   frames_written; // number of pictures written (or, returned)
};
typedef struct h262_filter_context *h262_filter_context_p;
#define SIZEOF_H262_FILTER_CONTEXT sizeof(struct h262_filter_context)

// ------------------------------------------------------------
struct h264_filter_context
{
  access_unit_context_p  access_unit_context;  // our "reader" for access units
  int   filter;  // TRUE if filtering, FALSE if stripping
  int   freq;    // Frequency of frames to try to keep if filtering
  int   allref;  // Keep all reference pictures

  // When filtering, we want:
  // a rolling count to compare with the desired frequency
  int   count;
  // `skipped_ref_pic` is TRUE if we've skipped any reference pictures
  // since our last IDR.
  int  skipped_ref_pic;
  // `last_accepted_was_not_IDR` is TRUE if the last frame kept (output)
  // was not an IDR. We set it TRUE initially so that we will decide
  // to output the first IDR we *do* find, regardless of the count.
  int  last_accepted_was_not_IDR;
  int  had_previous_access_unit;

  // Have we had an IDR in this run of the filter?
  int  not_had_IDR;

  int  frames_seen;    // number seen this filter run
  int  frames_written; // number written (or, returned)
};
typedef struct h264_filter_context *h264_filter_context_p;
#define SIZEOF_H264_FILTER_CONTEXT sizeof(struct h264_filter_context)

#endif // _filter_defns

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