gstreamer/gst-libs/gst/codecparsers/gstmpegvideoparser.c

/* Gstreamer
 * Copyright (C) <2011> Intel Corporation
 * Copyright (C) <2011> Collabora Ltd.
 * Copyright (C) <2011> Thibault Saunier <thibault.saunier@collabora.com>
 *
 * From bad/sys/vdpau/mpeg/mpegutil.c:
 *   Copyright (C) <2007> Jan Schmidt <thaytan@mad.scientist.com>
 *   Copyright (C) <2009> Carl-Anton Ingmarsson <ca.ingmarsson@gmail.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/**
 * SECTION:gstmpegvideoparser
 * @short_description: Convenience library for mpeg1 and 2 video
 * bitstream parsing.
 *
 * <refsect2>
 * <para>
 * Provides useful functions for mpeg videos bitstream parsing.
 * </para>
 * </refsect2>
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include "gstmpegvideoparser.h"

#include <string.h>
#include <gst/base/gstbitreader.h>
#include <gst/base/gstbytereader.h>

#define MARKER_BIT 0x1

#define GET_BITS(b, num, bits) G_STMT_START {        \
  if (!gst_bit_reader_get_bits_uint32(b, bits, num)) \
    goto failed;                                     \
  GST_TRACE ("parsed %d bits: %d", num, *(bits));    \
} G_STMT_END

#define READ_UINT8(br, val, nbits) G_STMT_START {  \
  if (!gst_bit_reader_get_bits_uint8 (br, &val, nbits)) { \
    GST_WARNING ("failed to read uint8, nbits: %d", nbits); \
    goto failed; \
  } \
} G_STMT_END

#define READ_UINT16(br, val, nbits) G_STMT_START { \
  if (!gst_bit_reader_get_bits_uint16 (br, &val, nbits)) { \
    GST_WARNING ("failed to read uint16, nbits: %d", nbits); \
    goto failed; \
  } \
} G_STMT_END

#define READ_UINT32(br, val, nbits) G_STMT_START { \
  if (!gst_bit_reader_get_bits_uint32 (br, &val, nbits)) { \
    GST_WARNING ("failed to read uint32, nbits: %d", nbits); \
    goto failed; \
  } \
} G_STMT_END

/* default intra quant matrix, in zig-zag order */
const guint8 default_intra_quantizer_matrix[64] = {
  8,
  16, 16,
  19, 16, 19,
  22, 22, 22, 22,
  22, 22, 26, 24, 26,
  27, 27, 27, 26, 26, 26,
  26, 27, 27, 27, 29, 29, 29,
  34, 34, 34, 29, 29, 29, 27, 27,
  29, 29, 32, 32, 34, 34, 37,
  38, 37, 35, 35, 34, 35,
  38, 38, 40, 40, 40,
  48, 48, 46, 46,
  56, 56, 58,
  69, 69,
  83
};

const guint8 mpeg_zigzag_8x8[64] = {
  0, 1, 8, 16, 9, 2, 3, 10,
  17, 24, 32, 25, 18, 11, 4, 5,
  12, 19, 26, 33, 40, 48, 41, 34,
  27, 20, 13, 6, 7, 14, 21, 28,
  35, 42, 49, 56, 57, 50, 43, 36,
  29, 22, 15, 23, 30, 37, 44, 51,
  58, 59, 52, 45, 38, 31, 39, 46,
  53, 60, 61, 54, 47, 55, 62, 63
};

GST_DEBUG_CATEGORY (mpegvideo_parser_debug);
#define GST_CAT_DEFAULT mpegvideo_parser_debug

static gboolean initialized = FALSE;

static inline gboolean
find_start_code (GstBitReader * b)
{
  guint32 bits;

  /* 0 bits until byte aligned */
  while (b->bit != 0) {
    GET_BITS (b, 1, &bits);
  }

  /* 0 bytes until startcode */
  while (gst_bit_reader_peek_bits_uint32 (b, &bits, 32)) {
    if (bits >> 8 == 0x1) {
      return TRUE;
    } else {
      gst_bit_reader_skip (b, 8);
    }
  }

  return FALSE;

failed:
  return FALSE;
}

/* Set the Pixel Aspect Ratio in our hdr from a DAR code in the data */
static void
set_par_from_dar (GstMpegVideoSequenceHdr * seqhdr, guint8 asr_code)
{
  /* Pixel_width = DAR_width * display_vertical_size */
  /* Pixel_height = DAR_height * display_horizontal_size */
  switch (asr_code) {
    case 0x02:                 /* 3:4 DAR = 4:3 pixels */
      seqhdr->par_w = 4 * seqhdr->height;
      seqhdr->par_h = 3 * seqhdr->width;
      break;
    case 0x03:                 /* 9:16 DAR */
      seqhdr->par_w = 16 * seqhdr->height;
      seqhdr->par_h = 9 * seqhdr->width;
      break;
    case 0x04:                 /* 1:2.21 DAR */
      seqhdr->par_w = 221 * seqhdr->height;
      seqhdr->par_h = 100 * seqhdr->width;
      break;
    case 0x01:                 /* Square pixels */
      seqhdr->par_w = seqhdr->par_h = 1;
      break;
    default:
      GST_DEBUG ("unknown/invalid aspect_ratio_information %d", asr_code);
      break;
  }
}

static void
set_fps_from_code (GstMpegVideoSequenceHdr * seqhdr, guint8 fps_code)
{
  const gint framerates[][2] = {
    {30, 1}, {24000, 1001}, {24, 1}, {25, 1},
    {30000, 1001}, {30, 1}, {50, 1}, {60000, 1001},
    {60, 1}, {30, 1}
  };

  if (fps_code && fps_code < 10) {
    seqhdr->fps_n = framerates[fps_code][0];
    seqhdr->fps_d = framerates[fps_code][1];
  } else {
    GST_DEBUG ("unknown/invalid frame_rate_code %d", fps_code);
    /* Force a valid framerate */
    /* FIXME or should this be kept unknown ?? */
    seqhdr->fps_n = 30000;
    seqhdr->fps_d = 1001;
  }
}

static gboolean
gst_mpeg_video_parse_sequence (GstMpegVideoSequenceHdr * seqhdr,
    GstBitReader * br)
{
  guint8 bits;
  guint8 load_intra_flag, load_non_intra_flag;

  /* Setting the height/width codes */
  READ_UINT16 (br, seqhdr->width, 12);
  READ_UINT16 (br, seqhdr->height, 12);

  READ_UINT8 (br, seqhdr->aspect_ratio_info, 4);
  set_par_from_dar (seqhdr, seqhdr->aspect_ratio_info);

  READ_UINT8 (br, seqhdr->frame_rate_code, 4);
  set_fps_from_code (seqhdr, seqhdr->frame_rate_code);

  READ_UINT32 (br, seqhdr->bitrate_value, 18);
  if (seqhdr->bitrate_value == 0x3ffff) {
    /* VBR stream */
    seqhdr->bitrate = 0;
  } else {
    /* Value in header is in units of 400 bps */
    seqhdr->bitrate *= 400;
  }

  READ_UINT8 (br, bits, 1);
  if (bits != MARKER_BIT)
    goto failed;

  /* VBV buffer size */
  READ_UINT16 (br, seqhdr->vbv_buffer_size_value, 10);

  /* constrained_parameters_flag */
  READ_UINT8 (br, seqhdr->constrained_parameters_flag, 1);

  /* load_intra_quantiser_matrix */
  READ_UINT8 (br, load_intra_flag, 1);
  if (load_intra_flag) {
    gint i;
    for (i = 0; i < 64; i++)
      READ_UINT8 (br, seqhdr->intra_quantizer_matrix[mpeg_zigzag_8x8[i]], 8);
  } else
    memcpy (seqhdr->intra_quantizer_matrix, default_intra_quantizer_matrix, 64);

  /* non intra quantizer matrix */
  READ_UINT8 (br, load_non_intra_flag, 1);
  if (load_non_intra_flag) {
    gint i;
    for (i = 0; i < 64; i++)
      READ_UINT8 (br, seqhdr->non_intra_quantizer_matrix[mpeg_zigzag_8x8[i]],
          8);
  } else
    memset (seqhdr->non_intra_quantizer_matrix, 16, 64);

  /* dump some info */
  GST_LOG ("width x height: %d x %d", seqhdr->width, seqhdr->height);
  GST_LOG ("fps: %d/%d", seqhdr->fps_n, seqhdr->fps_d);
  GST_LOG ("par: %d/%d", seqhdr->par_w, seqhdr->par_h);
  GST_LOG ("bitrate: %d", seqhdr->bitrate);

  return TRUE;

  /* ERRORS */
failed:
  {
    GST_WARNING ("Failed to parse sequence header");
    /* clear out stuff */
    memset (seqhdr, 0, sizeof (*seqhdr));
    return FALSE;
  }
}

static inline guint
scan_for_start_codes (const GstByteReader * reader, guint offset, guint size)
{
  const guint8 *data;
  guint32 state;
  guint i;

  g_return_val_if_fail (size > 0, -1);
  g_return_val_if_fail ((guint64) offset + size <= reader->size - reader->byte,
      -1);

  /* we can't find the pattern with less than 4 bytes */
  if (G_UNLIKELY (size < 4))
    return -1;

  data = reader->data + reader->byte + offset;

  /* set the state to something that does not match */
  state = 0xffffffff;

  /* now find data */
  for (i = 0; i < size; i++) {
    /* throw away one byte and move in the next byte */
    state = ((state << 8) | data[i]);
    if (G_UNLIKELY ((state & 0xffffff00) == 0x00000100)) {
      /* we have a match but we need to have skipped at
       * least 4 bytes to fill the state. */
      if (G_LIKELY (i >= 3))
        return offset + i - 3;
    }

    /* TODO: reimplement making 010001 not detected as a sc
     * Accelerate search for start code
     * if (data[i] > 1) {
     * while (i < (size - 4) && data[i] > 1) {
     *   if (data[i + 3] > 1)
     *     i += 4;
     *   else
     *     i += 1;
     * }
     * state = 0x00000100;
     *}
     */
  }

  /* nothing found */
  return -1;
}

/****** API *******/

/**
 * gst_mpeg_video_parse:
 * @data: The data to parse
 * @size: The size of @data
 * @offset: The offset from which to start parsing
 *
 * Parses the MPEG 1/2 video bitstream contained in @data , and returns the
 * detect packets as a list of #GstMpegVideoTypeOffsetSize.
 *
 * Returns: a #GList of #GstMpegVideoTypeOffsetSize
 */
GList *
gst_mpeg_video_parse (const guint8 * data, gsize size, guint offset)
{
  gint off, rsize;
  GstByteReader br;
  GList *ret = NULL;

  size -= offset;

  if (!initialized) {
    GST_DEBUG_CATEGORY_INIT (mpegvideo_parser_debug, "codecparsers_mpegvideo",
        0, "Mpegvideo parser library");
    initialized = TRUE;
  }

  if (size <= 0) {
    GST_DEBUG ("Can't parse from offset %d, buffer is to small", offset);
    return NULL;
  }

  gst_byte_reader_init (&br, &data[offset], size);

  off = scan_for_start_codes (&br, 0, size);

  if (off < 0) {
    GST_DEBUG ("No start code prefix in this buffer");
    return NULL;
  }

  while (off >= 0 && off + 3 < size) {
    GstMpegVideoTypeOffsetSize *codoffsize;

    gst_byte_reader_skip (&br, off + 3);

    codoffsize = g_malloc (sizeof (GstMpegVideoTypeOffsetSize));
    gst_byte_reader_get_uint8 (&br, &codoffsize->type);

    codoffsize->offset = gst_byte_reader_get_pos (&br) + offset;

    rsize = gst_byte_reader_get_remaining (&br);
    if (rsize <= 0)
      break;

    off = scan_for_start_codes (&br, 0, rsize);

    codoffsize->size = off;

    ret = g_list_prepend (ret, codoffsize);
    codoffsize = ret->data;
  }

  return g_list_reverse (ret);
}

/**
 * gst_mpeg_video_parse_sequence_header:
 * @seqhdr: (out): The #GstMpegVideoSequenceHdr structure to fill
 * @data: The data from which to parse the sequence header
 * @size: The size of @data
 * @offset: The offset in byte from which to start parsing @data
 *
 * Parses the @seqhdr Mpeg Video Sequence Header structure members from @data
 *
 * Returns: %TRUE if the seqhdr could be parsed correctly, %FALSE otherwize.
 */
gboolean
gst_mpeg_video_parse_sequence_header (GstMpegVideoSequenceHdr * seqhdr,
    const guint8 * data, gsize size, guint offset)
{
  GstBitReader br;

  g_return_val_if_fail (seqhdr != NULL, FALSE);

  size -= offset;

  if (size < 4)
    return FALSE;

  gst_bit_reader_init (&br, &data[offset], size);

  return gst_mpeg_video_parse_sequence (seqhdr, &br);
}

/**
 * gst_mpeg_video_parse_sequence_extension:
 * @seqext: (out): The #GstMpegVideoSequenceExt structure to fill
 * @data: The data from which to parse the sequence extension
 * @size: The size of @data
 * @offset: The offset in byte from which to start parsing @data
 *
 * Parses the @seqext Mpeg Video Sequence Extension structure members from @data
 *
 * Returns: %TRUE if the seqext could be parsed correctly, %FALSE otherwize.
 */
gboolean
gst_mpeg_video_parse_sequence_extension (GstMpegVideoSequenceExt * seqext,
    const guint8 * data, gsize size, guint offset)
{
  GstBitReader br;

  g_return_val_if_fail (seqext != NULL, FALSE);

  size -= offset;

  if (size < 6) {
    GST_DEBUG ("not enough bytes to parse the extension");
    return FALSE;
  }

  gst_bit_reader_init (&br, &data[offset], size);

  if (gst_bit_reader_get_bits_uint8_unchecked (&br, 4) !=
      GST_MPEG_VIDEO_PACKET_EXT_SEQUENCE) {
    GST_DEBUG ("Not parsing a sequence extension");
    return FALSE;
  }

  /* skip profile and level escape bit */
  gst_bit_reader_skip_unchecked (&br, 1);

  seqext->profile = gst_bit_reader_get_bits_uint8_unchecked (&br, 3);
  seqext->level = gst_bit_reader_get_bits_uint8_unchecked (&br, 4);

  /* progressive */
  seqext->progressive = gst_bit_reader_get_bits_uint8_unchecked (&br, 1);

  /* chroma format */
  seqext->chroma_format = gst_bit_reader_get_bits_uint8_unchecked (&br, 2);

  /* resolution extension */
  seqext->horiz_size_ext = gst_bit_reader_get_bits_uint8_unchecked (&br, 2);
  seqext->vert_size_ext = gst_bit_reader_get_bits_uint8_unchecked (&br, 2);

  seqext->bitrate_ext = gst_bit_reader_get_bits_uint16_unchecked (&br, 12);

  /* skip marker bits */
  gst_bit_reader_skip_unchecked (&br, 1);

  seqext->vbv_buffer_size_extension =
      gst_bit_reader_get_bits_uint8_unchecked (&br, 8);
  seqext->low_delay = gst_bit_reader_get_bits_uint8_unchecked (&br, 1);

  /* framerate extension */
  seqext->fps_n_ext = gst_bit_reader_get_bits_uint8_unchecked (&br, 2);
  seqext->fps_d_ext = gst_bit_reader_get_bits_uint8_unchecked (&br, 2);

  return TRUE;
}

/**
 * gst_mpeg_video_parse_quant_matrix_extension:
 * @quant: (out): The #GstMpegVideoQuantMatrixExt structure to fill
 * @data: The data from which to parse the Quantization Matrix extension
 * @size: The size of @data
 * @offset: The offset in byte from which to start the parsing
 *
 * Parses the @quant Mpeg Video Quant Matrix Extension structure members from
 * @data
 *
 * Returns: %TRUE if the quant matrix extension could be parsed correctly,
 * %FALSE otherwize.
 */
gboolean
gst_mpeg_video_parse_quant_matrix_extension (GstMpegVideoQuantMatrixExt * quant,
    const guint8 * data, gsize size, guint offset)
{
  guint8 i;
  GstBitReader br;

  g_return_val_if_fail (quant != NULL, FALSE);

  size -= offset;

  if (size < 1) {
    GST_DEBUG ("not enough bytes to parse the extension");
    return FALSE;
  }

  gst_bit_reader_init (&br, &data[offset], size);

  if (gst_bit_reader_get_bits_uint8_unchecked (&br, 4) !=
      GST_MPEG_VIDEO_PACKET_EXT_QUANT_MATRIX) {
    GST_DEBUG ("Not parsing a quant matrix extension");
    return FALSE;
  }

  READ_UINT8 (&br, quant->load_intra_quantiser_matrix, 1);
  if (quant->load_intra_quantiser_matrix) {
    for (i = 0; i < 64; i++) {
      READ_UINT8 (&br, quant->intra_quantiser_matrix[mpeg_zigzag_8x8[i]], 8);
    }
  }

  READ_UINT8 (&br, quant->load_non_intra_quantiser_matrix, 1);
  if (quant->load_non_intra_quantiser_matrix) {
    for (i = 0; i < 64; i++) {
      READ_UINT8 (&br, quant->non_intra_quantiser_matrix[mpeg_zigzag_8x8[i]],
          8);
    }
  }

  READ_UINT8 (&br, quant->load_chroma_intra_quantiser_matrix, 1);
  if (quant->load_chroma_intra_quantiser_matrix) {
    for (i = 0; i < 64; i++) {
      READ_UINT8 (&br, quant->chroma_intra_quantiser_matrix[mpeg_zigzag_8x8[i]],
          8);
    }
  }

  READ_UINT8 (&br, quant->load_chroma_non_intra_quantiser_matrix, 1);
  if (quant->load_chroma_non_intra_quantiser_matrix) {
    for (i = 0; i < 64; i++) {
      READ_UINT8 (&br,
          quant->chroma_non_intra_quantiser_matrix[mpeg_zigzag_8x8[i]], 8);
    }
  }

  return TRUE;

failed:
  GST_WARNING ("error parsing \"Quant Matrix Extension\"");
  return FALSE;
}

/**
 * gst_mpeg_video_parse_picture_extension:
 * @ext: (out): The #GstMpegVideoPictureExt structure to fill
 * @data: The data from which to parse the picture extension
 * @size: The size of @data
 * @offset: The offset in byte from which to start the parsing
 *
 * Parse the @ext Mpeg Video Picture Extension structure members from @data
 *
 * Returns: %TRUE if the picture extension could be parsed correctly,
 * %FALSE otherwize.
 */
gboolean
gst_mpeg_video_parse_picture_extension (GstMpegVideoPictureExt * ext,
    const guint8 * data, gsize size, guint offset)
{
  GstBitReader br;

  g_return_val_if_fail (ext != NULL, FALSE);

  size -= offset;

  if (size < 4)
    return FALSE;

  gst_bit_reader_init (&br, &data[offset], size);

  if (gst_bit_reader_get_bits_uint8_unchecked (&br, 4) !=
      GST_MPEG_VIDEO_PACKET_EXT_PICTURE) {
    GST_DEBUG ("Not parsing a picture extension");
    return FALSE;
  }

  /* f_code */
  READ_UINT8 (&br, ext->f_code[0][0], 4);
  READ_UINT8 (&br, ext->f_code[0][1], 4);
  READ_UINT8 (&br, ext->f_code[1][0], 4);
  READ_UINT8 (&br, ext->f_code[1][1], 4);

  /* intra DC precision */
  READ_UINT8 (&br, ext->intra_dc_precision, 2);

  /* picture structure */
  READ_UINT8 (&br, ext->picture_structure, 2);

  /* top field first */
  READ_UINT8 (&br, ext->top_field_first, 1);

  /* frame pred frame dct */
  READ_UINT8 (&br, ext->frame_pred_frame_dct, 1);

  /* concealment motion vectors */
  READ_UINT8 (&br, ext->concealment_motion_vectors, 1);

  /* q scale type */
  READ_UINT8 (&br, ext->q_scale_type, 1);

  /* intra vlc format */
  READ_UINT8 (&br, ext->intra_vlc_format, 1);

  /* alternate scan */
  READ_UINT8 (&br, ext->alternate_scan, 1);

  /* repeat first field */
  READ_UINT8 (&br, ext->repeat_first_field, 1);

  /* chroma_420_type */
  READ_UINT8 (&br, ext->chroma_420_type, 1);

  /* progressive_frame */
  READ_UINT8 (&br, ext->progressive_frame, 1);

  /* composite display */
  READ_UINT8 (&br, ext->composite_display, 1);

  if (ext->composite_display) {

    /* v axis */
    READ_UINT8 (&br, ext->v_axis, 1);

    /* field sequence */
    READ_UINT8 (&br, ext->field_sequence, 3);

    /* sub carrier */
    READ_UINT8 (&br, ext->sub_carrier, 1);

    /* burst amplitude */
    READ_UINT8 (&br, ext->burst_amplitude, 7);

    /* sub_carrier phase */
    READ_UINT8 (&br, ext->sub_carrier_phase, 8);
  }

  return TRUE;

failed:
  GST_WARNING ("error parsing \"Picture Coding Extension\"");
  return FALSE;

}

/**
 * gst_mpeg_video_parse_picture_header:
 * @hdr: (out): The #GstMpegVideoPictureHdr structure to fill
 * @data: The data from which to parse the picture header
 * @size: The size of @data
 * @offset: The offset in byte from which to start the parsing
 *
 * Parsers the @hdr Mpeg Video Picture Header structure members from @data
 *
 * Returns: %TRUE if the picture sequence could be parsed correctly, %FALSE
 * otherwize.
 */
gboolean
gst_mpeg_video_parse_picture_header (GstMpegVideoPictureHdr * hdr,
    const guint8 * data, gsize size, guint offset)
{
  GstBitReader br;

  size = size - offset;

  if (size < 4)
    goto failed;

  gst_bit_reader_init (&br, &data[offset], size);

  /* temperal sequence number */
  if (!gst_bit_reader_get_bits_uint16 (&br, &hdr->tsn, 10))
    goto failed;


  /* frame type */
  if (!gst_bit_reader_get_bits_uint8 (&br, (guint8 *) & hdr->pic_type, 3))
    goto failed;


  if (hdr->pic_type == 0 || hdr->pic_type > 4)
    goto failed;                /* Corrupted picture packet */

  /* skip VBV delay */
  if (!gst_bit_reader_skip (&br, 16))
    goto failed;

  if (hdr->pic_type == GST_MPEG_VIDEO_PICTURE_TYPE_P
      || hdr->pic_type == GST_MPEG_VIDEO_PICTURE_TYPE_B) {

    READ_UINT8 (&br, hdr->full_pel_forward_vector, 1);

    READ_UINT8 (&br, hdr->f_code[0][0], 3);
    hdr->f_code[0][1] = hdr->f_code[0][0];
  } else {
    hdr->full_pel_forward_vector = 0;
    hdr->f_code[0][0] = hdr->f_code[0][1] = 0;
  }

  if (hdr->pic_type == GST_MPEG_VIDEO_PICTURE_TYPE_B) {
    READ_UINT8 (&br, hdr->full_pel_backward_vector, 1);

    READ_UINT8 (&br, hdr->f_code[1][0], 3);
    hdr->f_code[1][1] = hdr->f_code[1][0];
  } else {
    hdr->full_pel_backward_vector = 0;
    hdr->f_code[1][0] = hdr->f_code[1][1] = 0;
  }

  return TRUE;

failed:
  {
    GST_WARNING ("Failed to parse picture header");
    return FALSE;
  }
}

/**
 * gst_mpeg_video_parse_gop:
 * @gop: (out): The #GstMpegVideoGop structure to fill
 * @data: The data from which to parse the gop
 * @size: The size of @data
 * @offset: The offset in byte from which to start the parsing
 *
 * Parses the @gop Mpeg Video Group of Picture structure members from @data
 *
 * Returns: %TRUE if the gop could be parsed correctly, %FALSE otherwize.
 */
gboolean
gst_mpeg_video_parse_gop (GstMpegVideoGop * gop, const guint8 * data,
    gsize size, guint offset)
{
  GstBitReader br;

  g_return_val_if_fail (gop != NULL, FALSE);

  size -= offset;

  if (size < 4)
    return FALSE;

  gst_bit_reader_init (&br, &data[offset], size);

  READ_UINT8 (&br, gop->drop_frame_flag, 1);

  READ_UINT8 (&br, gop->hour, 5);

  READ_UINT8 (&br, gop->minute, 6);

  /* skip unused bit */
  if (!gst_bit_reader_skip (&br, 1))
    return FALSE;

  READ_UINT8 (&br, gop->second, 6);

  READ_UINT8 (&br, gop->frame, 6);

  READ_UINT8 (&br, gop->closed_gop, 1);

  READ_UINT8 (&br, gop->broken_link, 1);

  return TRUE;

failed:
  GST_WARNING ("error parsing \"GOP\"");
  return FALSE;
}