ivfdec.c

/*
 *  Copyright (c) 2013 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "vpx_ports/mem_ops.h"

#include "./ivfdec.h"

static const char *IVF_SIGNATURE = "DKIF";

static void fix_framerate(int *num, int *den) {
  // Some versions of vpxenc used 1/(2*fps) for the timebase, so
  // we can guess the framerate using only the timebase in this
  // case. Other files would require reading ahead to guess the
  // timebase, like we do for webm.
  if (*num < 1000) {
    // Correct for the factor of 2 applied to the timebase in the encoder.
    if (*num & 1)
      *den *= 2;
    else
      *num /= 2;
  } else {
    // Don't know FPS for sure, and don't have readahead code
    // (yet?), so just default to 30fps.
    *num = 30;
    *den = 1;
  }
}

int file_is_ivf(struct VpxInputContext *input_ctx) {
  char raw_hdr[32];
  int is_ivf = 0;

  if (fread(raw_hdr, 1, 32, input_ctx->file) == 32) {
    if (memcmp(IVF_SIGNATURE, raw_hdr, 4) == 0) {
      is_ivf = 1;

      if (mem_get_le16(raw_hdr + 4) != 0) {
        fprintf(stderr, "Error: Unrecognized IVF version! This file may not"
                " decode properly.");
      }

      input_ctx->fourcc = mem_get_le32(raw_hdr + 8);
      input_ctx->width = mem_get_le16(raw_hdr + 12);
      input_ctx->height = mem_get_le16(raw_hdr + 14);
      input_ctx->framerate.numerator = mem_get_le32(raw_hdr + 16);
      input_ctx->framerate.denominator = mem_get_le32(raw_hdr + 20);
      fix_framerate(&input_ctx->framerate.numerator,
                    &input_ctx->framerate.denominator);
    }
  }

  if (!is_ivf) {
    rewind(input_ctx->file);
    input_ctx->detect.buf_read = 0;
  } else {
    input_ctx->detect.position = 4;
  }
  return is_ivf;
}