gstreamer/gst-libs/gst/vaapi/gstvaapidecoder_mpeg2.c

/*
 *  gstvaapidecoder_mpeg2.c - MPEG-2 decoder
 *
 *  Copyright (C) 2011 Intel Corporation
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public License
 *  as published by the Free Software Foundation; either version 2.1
 *  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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free
 *  Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 *  Boston, MA 02110-1301 USA
 */

/**
 * SECTION:gstvaapidecoder_mpeg2
 * @short_description: MPEG-2 decoder
 */

#include "sysdeps.h"
#include <string.h>
#include <gst/base/gstbitreader.h>
#include <gst/codecparsers/gstmpegvideoparser.h>
#include "gstvaapidecoder_mpeg2.h"
#include "gstvaapidecoder_objects.h"
#include "gstvaapidecoder_dpb.h"
#include "gstvaapidecoder_priv.h"
#include "gstvaapidisplay_priv.h"
#include "gstvaapiobject_priv.h"

#define DEBUG 1
#include "gstvaapidebug.h"

G_DEFINE_TYPE(GstVaapiDecoderMpeg2,
              gst_vaapi_decoder_mpeg2,
              GST_VAAPI_TYPE_DECODER)

#define GST_VAAPI_DECODER_MPEG2_GET_PRIVATE(obj)                \
    (G_TYPE_INSTANCE_GET_PRIVATE((obj),                         \
                                 GST_VAAPI_TYPE_DECODER_MPEG2,  \
                                 GstVaapiDecoderMpeg2Private))

#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 SKIP(reader, nbits) G_STMT_START { \
  if (!gst_bit_reader_skip (reader, nbits)) { \
    GST_WARNING ("failed to skip nbits: %d", nbits); \
    goto failed; \
  } \
} G_STMT_END

/* PTS Generator */
typedef struct _PTSGenerator PTSGenerator;
struct _PTSGenerator {
    GstClockTime        gop_pts; // Current GOP PTS
    GstClockTime        max_pts; // Max picture PTS
    guint               gop_tsn; // Absolute GOP TSN
    guint               max_tsn; // Max picture TSN, relative to last GOP TSN
    guint               ovl_tsn; // How many times TSN overflowed since GOP
    guint               lst_tsn; // Last picture TSN
    guint               fps_n;
    guint               fps_d;
};

static void
pts_init(PTSGenerator *tsg)
{
    tsg->gop_pts = GST_CLOCK_TIME_NONE;
    tsg->max_pts = GST_CLOCK_TIME_NONE;
    tsg->gop_tsn = 0;
    tsg->max_tsn = 0;
    tsg->ovl_tsn = 0;
    tsg->lst_tsn = 0;
    tsg->fps_n   = 0;
    tsg->fps_d   = 0;
}

static inline GstClockTime
pts_get_duration(PTSGenerator *tsg, guint num_frames)
{
    return gst_util_uint64_scale(num_frames,
                                 GST_SECOND * tsg->fps_d, tsg->fps_n);
}

static inline guint
pts_get_poc(PTSGenerator *tsg)
{
    return tsg->gop_tsn + tsg->ovl_tsn * 1024 + tsg->lst_tsn;
}

static void
pts_set_framerate(PTSGenerator *tsg, guint fps_n, guint fps_d)
{
    tsg->fps_n = fps_n;
    tsg->fps_d = fps_d;
}

static void
pts_sync(PTSGenerator *tsg, GstClockTime gop_pts)
{
    guint gop_tsn;

    if (!GST_CLOCK_TIME_IS_VALID(gop_pts) ||
        (GST_CLOCK_TIME_IS_VALID(tsg->max_pts) && tsg->max_pts >= gop_pts)) {
        /* Invalid GOP PTS, interpolate from the last known picture PTS */
        if (GST_CLOCK_TIME_IS_VALID(tsg->max_pts)) {
            gop_pts = tsg->max_pts + pts_get_duration(tsg, 1);
            gop_tsn = tsg->gop_tsn + tsg->ovl_tsn * 1024 + tsg->max_tsn + 1;
        }
        else {
            gop_pts = 0;
            gop_tsn = 0;
        }
    }
    else {
        /* Interpolate GOP TSN from this valid PTS */
        if (GST_CLOCK_TIME_IS_VALID(tsg->gop_pts))
            gop_tsn = tsg->gop_tsn + gst_util_uint64_scale(
                gop_pts - tsg->gop_pts + pts_get_duration(tsg, 1) - 1,
                tsg->fps_n, GST_SECOND * tsg->fps_d);
        else
            gop_tsn = 0;
    }

    tsg->gop_pts = gop_pts;
    tsg->gop_tsn = gop_tsn;
    tsg->max_tsn = 0;
    tsg->ovl_tsn = 0;
    tsg->lst_tsn = 0;
}

static GstClockTime
pts_eval(PTSGenerator *tsg, GstClockTime pic_pts, guint pic_tsn)
{
    GstClockTime pts;

    if (!GST_CLOCK_TIME_IS_VALID(tsg->gop_pts))
        tsg->gop_pts = 0;

    pts = tsg->gop_pts + pts_get_duration(tsg, tsg->ovl_tsn * 1024 + pic_tsn);

    if (!GST_CLOCK_TIME_IS_VALID(tsg->max_pts) || tsg->max_pts < pts)
        tsg->max_pts = pts;

    if (tsg->max_tsn < pic_tsn)
        tsg->max_tsn = pic_tsn;
    else if (tsg->max_tsn == 1023 && pic_tsn < tsg->lst_tsn) { /* TSN wrapped */
        tsg->max_tsn = pic_tsn;
        tsg->ovl_tsn++;
    }
    tsg->lst_tsn = pic_tsn;
    return pts;
}

struct _GstVaapiDecoderMpeg2Private {
    GstVaapiProfile             profile;
    GstVaapiProfile             hw_profile;
    guint                       width;
    guint                       height;
    guint                       fps_n;
    guint                       fps_d;
    GstMpegVideoSequenceHdr     seq_hdr;
    GstMpegVideoSequenceExt     seq_ext;
    GstMpegVideoPictureHdr      pic_hdr;
    GstMpegVideoPictureExt      pic_ext;
    GstMpegVideoQuantMatrixExt  quant_matrix_ext;
    GstVaapiPicture            *current_picture;
    GstVaapiDpb                *dpb;
    GstAdapter                 *adapter;
    PTSGenerator                tsg;
    guint                       is_constructed          : 1;
    guint                       is_opened               : 1;
    guint                       has_seq_ext             : 1;
    guint                       has_seq_scalable_ext    : 1;
    guint                       has_pic_ext             : 1;
    guint                       has_quant_matrix_ext    : 1;
    guint                       size_changed            : 1;
    guint                       profile_changed         : 1;
    guint                       quant_matrix_changed    : 1;
    guint                       progressive_sequence    : 1;
    guint                       closed_gop              : 1;
    guint                       broken_link             : 1;
};

/* VLC decoder from gst-plugins-bad */
typedef struct _VLCTable VLCTable;
struct _VLCTable {
    gint  value;
    guint cword;
    guint cbits;
};

static gboolean
decode_vlc(GstBitReader *br, gint *res, const VLCTable *table, guint length)
{
    guint8 i;
    guint cbits = 0;
    guint32 value = 0;

    for (i = 0; i < length; i++) {
        if (cbits != table[i].cbits) {
            cbits = table[i].cbits;
            if (!gst_bit_reader_peek_bits_uint32(br, &value, cbits)) {
                goto failed;
            }
        }

        if (value == table[i].cword) {
            SKIP(br, cbits);
            if (res)
                *res = table[i].value;
            return TRUE;
        }
    }
    GST_DEBUG("failed to find VLC code");

failed:
    GST_WARNING("failed to decode VLC, returning");
    return FALSE;
}

enum {
    GST_MPEG_VIDEO_MACROBLOCK_ESCAPE = -1,
};

/* Table B-1: Variable length codes for macroblock_address_increment */
static const VLCTable mpeg2_mbaddr_vlc_table[] = {
    {  1, 0x01,  1 },
    {  2, 0x03,  3 },
    {  3, 0x02,  3 },
    {  4, 0x03,  4 },
    {  5, 0x02,  4 },
    {  6, 0x03,  5 },
    {  7, 0x02,  5 },
    {  8, 0x07,  7 },
    {  9, 0x06,  7 },
    { 10, 0x0b,  8 },
    { 11, 0x0a,  8 },
    { 12, 0x09,  8 },
    { 13, 0x08,  8 },
    { 14, 0x07,  8 },
    { 15, 0x06,  8 },
    { 16, 0x17, 10 },
    { 17, 0x16, 10 },
    { 18, 0x15, 10 },
    { 19, 0x14, 10 },
    { 20, 0x13, 10 },
    { 21, 0x12, 10 },
    { 22, 0x23, 11 },
    { 23, 0x22, 11 },
    { 24, 0x21, 11 },
    { 25, 0x20, 11 },
    { 26, 0x1f, 11 },
    { 27, 0x1e, 11 },
    { 28, 0x1d, 11 },
    { 29, 0x1c, 11 },
    { 30, 0x1b, 11 },
    { 31, 0x1a, 11 },
    { 32, 0x19, 11 },
    { 33, 0x18, 11 },
    { GST_MPEG_VIDEO_MACROBLOCK_ESCAPE, 0x08, 11 }
};

static void
gst_vaapi_decoder_mpeg2_close(GstVaapiDecoderMpeg2 *decoder)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;

    gst_vaapi_picture_replace(&priv->current_picture, NULL);

    if (priv->dpb) {
        gst_vaapi_dpb_unref(priv->dpb);
        priv->dpb = NULL;
    }

    if (priv->adapter) {
        gst_adapter_clear(priv->adapter);
        g_object_unref(priv->adapter);
        priv->adapter = NULL;
    }
}

static gboolean
gst_vaapi_decoder_mpeg2_open(GstVaapiDecoderMpeg2 *decoder, GstBuffer *buffer)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;

    gst_vaapi_decoder_mpeg2_close(decoder);

    priv->adapter = gst_adapter_new();
    if (!priv->adapter)
	return FALSE;

    priv->dpb = gst_vaapi_dpb_mpeg2_new();
    if (!priv->dpb)
        return FALSE;

    pts_init(&priv->tsg);
    return TRUE;
}

static void
gst_vaapi_decoder_mpeg2_destroy(GstVaapiDecoderMpeg2 *decoder)
{
    gst_vaapi_decoder_mpeg2_close(decoder);
}

static gboolean
gst_vaapi_decoder_mpeg2_create(GstVaapiDecoderMpeg2 *decoder)
{
    if (!GST_VAAPI_DECODER_CODEC(decoder))
        return FALSE;
    return TRUE;
}

static inline void
copy_quant_matrix(guint8 dst[64], const guint8 src[64])
{
    memcpy(dst, src, 64);
}

static const char *
get_profile_str(GstVaapiProfile profile)
{
    char *str;

    switch (profile) {
    case GST_VAAPI_PROFILE_MPEG2_SIMPLE:    str = "simple";     break;
    case GST_VAAPI_PROFILE_MPEG2_MAIN:      str = "main";       break;
    case GST_VAAPI_PROFILE_MPEG2_HIGH:      str = "high";       break;
    default:                                str = "<unknown>";  break;
    }
    return str;
}

static GstVaapiProfile
get_profile(GstVaapiDecoderMpeg2 *decoder, GstVaapiEntrypoint entrypoint)
{
    GstVaapiDisplay * const va_display = GST_VAAPI_DECODER_DISPLAY(decoder);
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstVaapiProfile profile = priv->profile;

    do {
        /* Return immediately if the exact same profile was found */
        if (gst_vaapi_display_has_decoder(va_display, profile, entrypoint))
            break;

        /* Otherwise, try to map to a higher profile */
        switch (profile) {
        case GST_VAAPI_PROFILE_MPEG2_SIMPLE:
            profile = GST_VAAPI_PROFILE_MPEG2_MAIN;
            break;
        case GST_VAAPI_PROFILE_MPEG2_MAIN:
            profile = GST_VAAPI_PROFILE_MPEG2_HIGH;
            break;
        case GST_VAAPI_PROFILE_MPEG2_HIGH:
            // Try to map to main profile if no high profile specific bits used
            if (priv->profile == profile    &&
                !priv->has_seq_scalable_ext &&
                (priv->has_seq_ext && priv->seq_ext.chroma_format == 1)) {
                profile = GST_VAAPI_PROFILE_MPEG2_MAIN;
                break;
            }
            // fall-through
        default:
            profile = GST_VAAPI_PROFILE_UNKNOWN;
            break;
        }
    } while (profile != GST_VAAPI_PROFILE_UNKNOWN);

    if (profile != priv->profile)
        GST_INFO("forced %s profile to %s profile",
                 get_profile_str(priv->profile), get_profile_str(profile));
    return profile;
}

static GstVaapiDecoderStatus
ensure_context(GstVaapiDecoderMpeg2 *decoder)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstVaapiEntrypoint entrypoint = GST_VAAPI_ENTRYPOINT_VLD;
    gboolean reset_context = FALSE;

    if (priv->profile_changed) {
        GST_DEBUG("profile changed");
        priv->profile_changed = FALSE;
        reset_context         = TRUE;

        priv->hw_profile = get_profile(decoder, entrypoint);
        if (priv->hw_profile == GST_VAAPI_PROFILE_UNKNOWN)
            return GST_VAAPI_DECODER_STATUS_ERROR_UNSUPPORTED_PROFILE;
    }

    if (priv->size_changed) {
        GST_DEBUG("size changed");
        priv->size_changed = FALSE;
        reset_context      = TRUE;
    }

    if (reset_context) {
        GstVaapiContextInfo info;

        info.profile    = priv->hw_profile;
        info.entrypoint = entrypoint;
        info.width      = priv->width;
        info.height     = priv->height;
        info.ref_frames = 2;
        reset_context   = gst_vaapi_decoder_ensure_context(
            GST_VAAPI_DECODER(decoder),
            &info
        );
        if (!reset_context)
            return GST_VAAPI_DECODER_STATUS_ERROR_UNKNOWN;
    }
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static GstVaapiDecoderStatus
ensure_quant_matrix(GstVaapiDecoderMpeg2 *decoder, GstVaapiPicture *picture)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    VAIQMatrixBufferMPEG2 *iq_matrix;
    guint8 *intra_quant_matrix = NULL;
    guint8 *non_intra_quant_matrix = NULL;
    guint8 *chroma_intra_quant_matrix = NULL;
    guint8 *chroma_non_intra_quant_matrix = NULL;

    if (!priv->quant_matrix_changed)
        return GST_VAAPI_DECODER_STATUS_SUCCESS;

    priv->quant_matrix_changed = FALSE;

    picture->iq_matrix = GST_VAAPI_IQ_MATRIX_NEW(MPEG2, decoder);
    if (!picture->iq_matrix) {
        GST_ERROR("failed to allocate IQ matrix");
        return GST_VAAPI_DECODER_STATUS_ERROR_ALLOCATION_FAILED;
    }
    iq_matrix = picture->iq_matrix->param;

    intra_quant_matrix     = priv->seq_hdr.intra_quantizer_matrix;
    non_intra_quant_matrix = priv->seq_hdr.non_intra_quantizer_matrix;
    if (priv->has_quant_matrix_ext) {
        if (priv->quant_matrix_ext.load_intra_quantiser_matrix)
            intra_quant_matrix = priv->quant_matrix_ext.intra_quantiser_matrix;
        if (priv->quant_matrix_ext.load_non_intra_quantiser_matrix)
            non_intra_quant_matrix = priv->quant_matrix_ext.non_intra_quantiser_matrix;
        if (priv->quant_matrix_ext.load_chroma_intra_quantiser_matrix)
            chroma_intra_quant_matrix = priv->quant_matrix_ext.chroma_intra_quantiser_matrix;
        if (priv->quant_matrix_ext.load_chroma_non_intra_quantiser_matrix)
            chroma_non_intra_quant_matrix = priv->quant_matrix_ext.chroma_non_intra_quantiser_matrix;
    }

    iq_matrix->load_intra_quantiser_matrix = intra_quant_matrix != NULL;
    if (intra_quant_matrix)
        copy_quant_matrix(iq_matrix->intra_quantiser_matrix,
                          intra_quant_matrix);

    iq_matrix->load_non_intra_quantiser_matrix = non_intra_quant_matrix != NULL;
    if (non_intra_quant_matrix)
        copy_quant_matrix(iq_matrix->non_intra_quantiser_matrix,
                          non_intra_quant_matrix);

    iq_matrix->load_chroma_intra_quantiser_matrix = chroma_intra_quant_matrix != NULL;
    if (chroma_intra_quant_matrix)
        copy_quant_matrix(iq_matrix->chroma_intra_quantiser_matrix,
                          chroma_intra_quant_matrix);

    iq_matrix->load_chroma_non_intra_quantiser_matrix = chroma_non_intra_quant_matrix != NULL;
    if (chroma_non_intra_quant_matrix)
        copy_quant_matrix(iq_matrix->chroma_non_intra_quantiser_matrix,
                          chroma_non_intra_quant_matrix);
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static gboolean
decode_current_picture(GstVaapiDecoderMpeg2 *decoder)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstVaapiPicture * const picture = priv->current_picture;

    if (picture) {
        if (!gst_vaapi_picture_decode(picture))
            return FALSE;
        if (GST_VAAPI_PICTURE_IS_COMPLETE(picture)) {
            if (!gst_vaapi_dpb_add(priv->dpb, picture))
                return FALSE;
            gst_vaapi_picture_replace(&priv->current_picture, NULL);
        }
    }
    return TRUE;
}

static GstVaapiDecoderStatus
decode_sequence(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoder * const base_decoder = GST_VAAPI_DECODER(decoder);
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstMpegVideoSequenceHdr * const seq_hdr = &priv->seq_hdr;

    if (!gst_mpeg_video_parse_sequence_header(seq_hdr, buf, buf_size, 4)) {
        GST_ERROR("failed to parse sequence header");
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }

    priv->fps_n = seq_hdr->fps_n;
    priv->fps_d = seq_hdr->fps_d;
    pts_set_framerate(&priv->tsg, priv->fps_n, priv->fps_d);
    gst_vaapi_decoder_set_framerate(base_decoder, priv->fps_n, priv->fps_d);

    if (gst_mpeg_video_finalise_mpeg2_sequence_header(seq_hdr, NULL, NULL))
        gst_vaapi_decoder_set_pixel_aspect_ratio(base_decoder,
            seq_hdr->par_w, seq_hdr->par_h);

    priv->width                 = seq_hdr->width;
    priv->height                = seq_hdr->height;
    priv->has_seq_ext           = FALSE;
    priv->size_changed          = TRUE;
    priv->quant_matrix_changed  = TRUE;
    priv->progressive_sequence  = TRUE;
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static GstVaapiDecoderStatus
decode_sequence_ext(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoder * const base_decoder = GST_VAAPI_DECODER(decoder);
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstMpegVideoSequenceHdr * const seq_hdr = &priv->seq_hdr;
    GstMpegVideoSequenceExt * const seq_ext = &priv->seq_ext;
    GstVaapiProfile profile;
    guint width, height;

    if (!gst_mpeg_video_parse_sequence_extension(seq_ext, buf, buf_size, 4)) {
        GST_ERROR("failed to parse sequence-extension");
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }
    priv->has_seq_ext = TRUE;
    priv->progressive_sequence = seq_ext->progressive;
    gst_vaapi_decoder_set_interlaced(base_decoder, !priv->progressive_sequence);

    width  = (priv->width  & 0x0fff) | ((guint32)seq_ext->horiz_size_ext << 12);
    height = (priv->height & 0x0fff) | ((guint32)seq_ext->vert_size_ext  << 12);
    GST_DEBUG("video resolution %ux%u", width, height);

    if (seq_ext->fps_n_ext && seq_ext->fps_d_ext) {
        priv->fps_n *= seq_ext->fps_n_ext + 1;
        priv->fps_d *= seq_ext->fps_d_ext + 1;
        pts_set_framerate(&priv->tsg, priv->fps_n, priv->fps_d);
        gst_vaapi_decoder_set_framerate(base_decoder, priv->fps_n, priv->fps_d);
    }

    if (priv->width != width) {
        priv->width = width;
        priv->size_changed = TRUE;
    }

    if (priv->height != height) {
        priv->height = height;
        priv->size_changed = TRUE;
    }

    switch (seq_ext->profile) {
    case GST_MPEG_VIDEO_PROFILE_SIMPLE:
        profile = GST_VAAPI_PROFILE_MPEG2_SIMPLE;
        break;
    case GST_MPEG_VIDEO_PROFILE_MAIN:
        profile = GST_VAAPI_PROFILE_MPEG2_MAIN;
        break;
    case GST_MPEG_VIDEO_PROFILE_HIGH:
        profile = GST_VAAPI_PROFILE_MPEG2_HIGH;
        break;
    default:
        GST_ERROR("unsupported profile %d", seq_ext->profile);
        return GST_VAAPI_DECODER_STATUS_ERROR_UNSUPPORTED_PROFILE;
    }
    if (priv->profile != profile) {
        priv->profile = profile;
        priv->profile_changed = TRUE;
    }

    if (gst_mpeg_video_finalise_mpeg2_sequence_header(seq_hdr, seq_ext, NULL))
        gst_vaapi_decoder_set_pixel_aspect_ratio(base_decoder,
            seq_hdr->par_w, seq_hdr->par_h);

    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static GstVaapiDecoderStatus
decode_sequence_end(GstVaapiDecoderMpeg2 *decoder)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;

    if (priv->current_picture && !decode_current_picture(decoder))
        return GST_VAAPI_DECODER_STATUS_ERROR_UNKNOWN;

    gst_vaapi_dpb_flush(priv->dpb);
    return GST_VAAPI_DECODER_STATUS_END_OF_STREAM;
}

static GstVaapiDecoderStatus
decode_quant_matrix_ext(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstMpegVideoQuantMatrixExt * const quant_matrix_ext = &priv->quant_matrix_ext;

    if (!gst_mpeg_video_parse_quant_matrix_extension(quant_matrix_ext, buf, buf_size, 4)) {
        GST_ERROR("failed to parse quant-matrix-extension");
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }
    priv->has_quant_matrix_ext = TRUE;
    priv->quant_matrix_changed = TRUE;
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static GstVaapiDecoderStatus
decode_gop(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstMpegVideoGop gop;
    GstClockTime pts;

    if (!gst_mpeg_video_parse_gop(&gop, buf, buf_size, 4)) {
        GST_ERROR("failed to parse GOP");
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }

    priv->closed_gop  = gop.closed_gop;
    priv->broken_link = gop.broken_link;

    GST_DEBUG("GOP %02u:%02u:%02u:%02u (closed_gop %d, broken_link %d)",
              gop.hour, gop.minute, gop.second, gop.frame,
              priv->closed_gop, priv->broken_link);

    pts = gst_adapter_prev_timestamp(priv->adapter, NULL);
    pts_sync(&priv->tsg, pts);
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static GstVaapiDecoderStatus
decode_picture(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstMpegVideoPictureHdr * const pic_hdr = &priv->pic_hdr;
    GstVaapiPicture *picture;
    GstVaapiDecoderStatus status;
    GstClockTime pts;

    status = ensure_context(decoder);
    if (status != GST_VAAPI_DECODER_STATUS_SUCCESS) {
        GST_ERROR("failed to reset context");
        return status;
    }

    if (priv->current_picture && !decode_current_picture(decoder))
        return GST_VAAPI_DECODER_STATUS_ERROR_UNKNOWN;

    if (priv->current_picture) {
        /* Re-use current picture where the first field was decoded */
        picture = gst_vaapi_picture_new_field(priv->current_picture);
        if (!picture) {
            GST_ERROR("failed to allocate field picture");
            return GST_VAAPI_DECODER_STATUS_ERROR_ALLOCATION_FAILED;
        }
    }
    else {
        /* Create new picture */
        picture = GST_VAAPI_PICTURE_NEW(MPEG2, decoder);
        if (!picture) {
            GST_ERROR("failed to allocate picture");
            return GST_VAAPI_DECODER_STATUS_ERROR_ALLOCATION_FAILED;
        }
    }
    gst_vaapi_picture_replace(&priv->current_picture, picture);
    gst_vaapi_picture_unref(picture);

    status = ensure_quant_matrix(decoder, picture);
    if (status != GST_VAAPI_DECODER_STATUS_SUCCESS) {
        GST_ERROR("failed to reset quantizer matrix");
        return status;
    }

    if (!gst_mpeg_video_parse_picture_header(pic_hdr, buf, buf_size, 4)) {
        GST_ERROR("failed to parse picture header");
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }
    priv->has_pic_ext = FALSE;

    switch (pic_hdr->pic_type) {
    case GST_MPEG_VIDEO_PICTURE_TYPE_I:
        GST_VAAPI_PICTURE_FLAG_SET(picture, GST_VAAPI_PICTURE_FLAG_REFERENCE);
        picture->type = GST_VAAPI_PICTURE_TYPE_I;
        break;
    case GST_MPEG_VIDEO_PICTURE_TYPE_P:
        GST_VAAPI_PICTURE_FLAG_SET(picture, GST_VAAPI_PICTURE_FLAG_REFERENCE);
        picture->type = GST_VAAPI_PICTURE_TYPE_P;
        break;
    case GST_MPEG_VIDEO_PICTURE_TYPE_B:
        picture->type = GST_VAAPI_PICTURE_TYPE_B;
        break;
    default:
        GST_ERROR("unsupported picture type %d", pic_hdr->pic_type);
        return GST_VAAPI_DECODER_STATUS_ERROR_UNKNOWN;
    }

    /* Update presentation time */
    pts = gst_adapter_prev_timestamp(priv->adapter, NULL);
    picture->pts = pts_eval(&priv->tsg, pts, pic_hdr->tsn);
    picture->poc = pts_get_poc(&priv->tsg);
    return status;
}

static GstVaapiDecoderStatus
decode_picture_ext(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstMpegVideoPictureExt * const pic_ext = &priv->pic_ext;
    GstVaapiPicture * const picture = priv->current_picture;

    if (!gst_mpeg_video_parse_picture_extension(pic_ext, buf, buf_size, 4)) {
        GST_ERROR("failed to parse picture-extension");
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }
    priv->has_pic_ext = TRUE;

    if (priv->progressive_sequence && !pic_ext->progressive_frame) {
        GST_WARNING("invalid interlaced frame in progressive sequence, fixing");
        pic_ext->progressive_frame = 1;
    }

    if (pic_ext->picture_structure == 0 ||
        (pic_ext->progressive_frame &&
         pic_ext->picture_structure != GST_MPEG_VIDEO_PICTURE_STRUCTURE_FRAME)) {
        GST_WARNING("invalid picture_structure %d, replacing with \"frame\"",
                    pic_ext->picture_structure);
        pic_ext->picture_structure = GST_MPEG_VIDEO_PICTURE_STRUCTURE_FRAME;
    }

    if (!priv->progressive_sequence && !pic_ext->progressive_frame) {
        GST_VAAPI_PICTURE_FLAG_SET(picture, GST_VAAPI_PICTURE_FLAG_INTERLACED);
        if (pic_ext->top_field_first)
            GST_VAAPI_PICTURE_FLAG_SET(picture, GST_VAAPI_PICTURE_FLAG_TFF);
    }

    switch (pic_ext->picture_structure) {
    case GST_MPEG_VIDEO_PICTURE_STRUCTURE_TOP_FIELD:
        picture->structure = GST_VAAPI_PICTURE_STRUCTURE_TOP_FIELD;
        break;
    case GST_MPEG_VIDEO_PICTURE_STRUCTURE_BOTTOM_FIELD:
        picture->structure = GST_VAAPI_PICTURE_STRUCTURE_BOTTOM_FIELD;
        break;
    case GST_MPEG_VIDEO_PICTURE_STRUCTURE_FRAME:
        picture->structure = GST_VAAPI_PICTURE_STRUCTURE_FRAME;
        break;
    }

    /* Allocate dummy picture for first field based I-frame */
    if (picture->type == GST_VAAPI_PICTURE_TYPE_I &&
        !GST_VAAPI_PICTURE_IS_FRAME(picture) &&
        gst_vaapi_dpb_size(priv->dpb) == 0) {
        GstVaapiPicture *dummy_picture;
        gboolean success;

        dummy_picture = GST_VAAPI_PICTURE_NEW(MPEG2, decoder);
        if (!dummy_picture) {
            GST_ERROR("failed to allocate dummy picture");
            return GST_VAAPI_DECODER_STATUS_ERROR_ALLOCATION_FAILED;
        }

        dummy_picture->type      = GST_VAAPI_PICTURE_TYPE_I;
        dummy_picture->pts       = GST_CLOCK_TIME_NONE;
        dummy_picture->poc       = -1;
        dummy_picture->structure = GST_VAAPI_PICTURE_STRUCTURE_FRAME;

        GST_VAAPI_PICTURE_FLAG_SET(
            dummy_picture,
            (GST_VAAPI_PICTURE_FLAG_SKIPPED |
             GST_VAAPI_PICTURE_FLAG_REFERENCE)
        );

        success = gst_vaapi_dpb_add(priv->dpb, dummy_picture);
        gst_vaapi_picture_unref(dummy_picture);
        if (!success) {
            GST_ERROR("failed to add dummy picture into DPB");
            return GST_VAAPI_DECODER_STATUS_ERROR_UNKNOWN;
        }
        GST_INFO("allocated dummy picture for first field based I-frame");
    }
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static inline guint32
pack_f_code(guint8 f_code[2][2])
{
    return (((guint32)f_code[0][0] << 12) |
            ((guint32)f_code[0][1] <<  8) |
            ((guint32)f_code[1][0] <<  4) |
            (         f_code[1][1]      ));
}

static gboolean
fill_picture(GstVaapiDecoderMpeg2 *decoder, GstVaapiPicture *picture)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    VAPictureParameterBufferMPEG2 * const pic_param = picture->param;
    GstMpegVideoPictureHdr * const pic_hdr = &priv->pic_hdr;
    GstMpegVideoPictureExt * const pic_ext = &priv->pic_ext;
    GstVaapiPicture *prev_picture, *next_picture;

    if (!priv->has_pic_ext)
        return FALSE;

    /* Fill in VAPictureParameterBufferMPEG2 */
    pic_param->horizontal_size                                          = priv->width;
    pic_param->vertical_size                                            = priv->height;
    pic_param->forward_reference_picture                                = VA_INVALID_ID;
    pic_param->backward_reference_picture                               = VA_INVALID_ID;
    pic_param->picture_coding_type                                      = pic_hdr->pic_type;
    pic_param->f_code                                                   = pack_f_code(pic_ext->f_code);

#define COPY_FIELD(a, b, f) \
    pic_param->a.b.f = pic_ext->f
    pic_param->picture_coding_extension.value                           = 0;
    pic_param->picture_coding_extension.bits.is_first_field             = GST_VAAPI_PICTURE_IS_FIRST_FIELD(picture);
    COPY_FIELD(picture_coding_extension, bits, intra_dc_precision);
    COPY_FIELD(picture_coding_extension, bits, picture_structure);
    COPY_FIELD(picture_coding_extension, bits, top_field_first);
    COPY_FIELD(picture_coding_extension, bits, frame_pred_frame_dct);
    COPY_FIELD(picture_coding_extension, bits, concealment_motion_vectors);
    COPY_FIELD(picture_coding_extension, bits, q_scale_type);
    COPY_FIELD(picture_coding_extension, bits, intra_vlc_format);
    COPY_FIELD(picture_coding_extension, bits, alternate_scan);
    COPY_FIELD(picture_coding_extension, bits, repeat_first_field);
    COPY_FIELD(picture_coding_extension, bits, progressive_frame);

    gst_vaapi_dpb_mpeg2_get_references(
        priv->dpb,
        picture,
        &prev_picture,
        &next_picture
    );

    switch (pic_hdr->pic_type) {
    case GST_MPEG_VIDEO_PICTURE_TYPE_B:
        if (next_picture)
            pic_param->backward_reference_picture = next_picture->surface_id;
        if (prev_picture)
            pic_param->forward_reference_picture = prev_picture->surface_id;
        else if (!priv->closed_gop)
            GST_VAAPI_PICTURE_FLAG_SET(picture, GST_VAAPI_PICTURE_FLAG_SKIPPED);
        break;
    case GST_MPEG_VIDEO_PICTURE_TYPE_P:
        if (prev_picture)
            pic_param->forward_reference_picture = prev_picture->surface_id;
        break;
    }
    return TRUE;
}

static GstVaapiDecoderStatus
decode_slice(
    GstVaapiDecoderMpeg2 *decoder,
    int                   slice_no,
    guchar               *buf,
    guint                 buf_size
)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstVaapiPicture * const picture = priv->current_picture;
    GstVaapiSlice *slice;
    VASliceParameterBufferMPEG2 *slice_param;
    GstBitReader br;
    gint mb_x, mb_y, mb_inc;
    guint macroblock_offset;
    guint8 slice_vertical_position_extension;
    guint8 quantiser_scale_code;
    guint8 intra_slice = 0;
    guint8 extra_bit_slice, junk8;

    GST_DEBUG("slice %d @ %p, %u bytes)", slice_no, buf, buf_size);

    if (picture->slices->len == 0 && !fill_picture(decoder, picture))
        return GST_VAAPI_DECODER_STATUS_ERROR_UNKNOWN;

    slice = GST_VAAPI_SLICE_NEW(MPEG2, decoder, buf, buf_size);
    if (!slice) {
        GST_ERROR("failed to allocate slice");
        return GST_VAAPI_DECODER_STATUS_ERROR_ALLOCATION_FAILED;
    }
    gst_vaapi_picture_add_slice(picture, slice);

    /* Parse slice */
    gst_bit_reader_init(&br, buf, buf_size);
    SKIP(&br, 32); /* slice_start_code */
    if (priv->height > 2800)
        READ_UINT8(&br, slice_vertical_position_extension, 3);
    if (priv->has_seq_scalable_ext) {
        GST_ERROR("failed to parse slice %d. Unsupported sequence_scalable_extension()", slice_no);
        return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
    }
    READ_UINT8(&br, quantiser_scale_code, 5);
    READ_UINT8(&br, extra_bit_slice, 1);
    if (extra_bit_slice == 1) {
        READ_UINT8(&br, intra_slice, 1);
        READ_UINT8(&br, junk8, 7);
        READ_UINT8(&br, extra_bit_slice, 1);
        while (extra_bit_slice == 1) {
            READ_UINT8(&br, junk8, 8);
            READ_UINT8(&br, extra_bit_slice, 1);
        }
    }
    macroblock_offset = gst_bit_reader_get_pos(&br);

    mb_y = slice_no;
    mb_x = -1;
    do {
        if (!decode_vlc(&br, &mb_inc, mpeg2_mbaddr_vlc_table,
                        G_N_ELEMENTS(mpeg2_mbaddr_vlc_table))) {
            GST_WARNING("failed to decode first macroblock_address_increment");
            goto failed;
        }
        mb_x += mb_inc == GST_MPEG_VIDEO_MACROBLOCK_ESCAPE ? 33 : mb_inc;
    } while (mb_inc == GST_MPEG_VIDEO_MACROBLOCK_ESCAPE);

    /* Fill in VASliceParameterBufferMPEG2 */
    slice_param                            = slice->param;
    slice_param->macroblock_offset         = macroblock_offset;
    slice_param->slice_horizontal_position = mb_x;
    slice_param->slice_vertical_position   = mb_y;
    slice_param->quantiser_scale_code      = quantiser_scale_code;
    slice_param->intra_slice_flag          = intra_slice;
    return GST_VAAPI_DECODER_STATUS_SUCCESS;

failed:
    return GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
}

static inline gint
scan_for_start_code(GstAdapter *adapter, guint ofs, guint size, guint32 *scp)
{
    return (gint)gst_adapter_masked_scan_uint32_peek(adapter,
                                                     0xffffff00, 0x00000100,
                                                     ofs, size,
                                                     scp);
}

static GstVaapiDecoderStatus
decode_packet(GstVaapiDecoderMpeg2 *decoder, guchar *buf, guint buf_size)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstVaapiDecoderStatus status;
    guchar type;

    /* The packet defined by buf and buf_size contains the start code */
    type = buf[3];
    switch (type) {
    case GST_MPEG_VIDEO_PACKET_PICTURE:
        if (!priv->width || !priv->height)
            goto unknown_picture_size;
        status = decode_picture(decoder, buf, buf_size);
        break;
    case GST_MPEG_VIDEO_PACKET_SEQUENCE:
        status = decode_sequence(decoder, buf, buf_size);
        break;
    case GST_MPEG_VIDEO_PACKET_EXTENSION: {
        const guchar id = buf[4] >> 4;
        switch (id) {
        case GST_MPEG_VIDEO_PACKET_EXT_SEQUENCE:
            status = decode_sequence_ext(decoder, buf, buf_size);
            break;
        case GST_MPEG_VIDEO_PACKET_EXT_QUANT_MATRIX:
            status = decode_quant_matrix_ext(decoder, buf, buf_size);
            break;
        case GST_MPEG_VIDEO_PACKET_EXT_PICTURE:
            if (!priv->width || !priv->height)
                goto unknown_picture_size;
            status = decode_picture_ext(decoder, buf, buf_size);
            break;
        default:
            // Ignore unknown start-code extensions
            GST_WARNING("unsupported start code extension (0x%02x)", id);
            status = GST_VAAPI_DECODER_STATUS_SUCCESS;
            break;
        }
        break;
    }
    case GST_MPEG_VIDEO_PACKET_SEQUENCE_END:
        status = decode_sequence_end(decoder);
        break;
    case GST_MPEG_VIDEO_PACKET_GOP:
        status = decode_gop(decoder, buf, buf_size);
        break;
    case GST_MPEG_VIDEO_PACKET_USER_DATA:
        // Ignore user-data packets
        status = GST_VAAPI_DECODER_STATUS_SUCCESS;
        break;
    default:
        if (type >= GST_MPEG_VIDEO_PACKET_SLICE_MIN &&
            type <= GST_MPEG_VIDEO_PACKET_SLICE_MAX) {
            if (!priv->current_picture)
                goto undefined_picture;
            status = decode_slice(
                decoder,
                type - GST_MPEG_VIDEO_PACKET_SLICE_MIN,
                buf, buf_size
            );
            break;
        }
        else if (type >= 0xb9 && type <= 0xff) {
            // Ignore system start codes (PES headers)
            status = GST_VAAPI_DECODER_STATUS_SUCCESS;
            break;
        }
        GST_WARNING("unsupported start code (0x%02x)", type);
        status = GST_VAAPI_DECODER_STATUS_ERROR_BITSTREAM_PARSER;
        break;
    }
    return status;

unknown_picture_size:
    // Ignore packet while picture size is undefined
    // i.e. missing sequence headers, or not parsed correctly
    GST_WARNING("failed to parse picture of unknown size");
    return GST_VAAPI_DECODER_STATUS_SUCCESS;

undefined_picture:
    // Ignore packet while picture is undefined
    // i.e. missing picture headers, or not parsed correctly
    GST_WARNING("failed to parse slice with undefined picture");
    return GST_VAAPI_DECODER_STATUS_SUCCESS;
}

static GstVaapiDecoderStatus
decode_buffer(GstVaapiDecoderMpeg2 *decoder, GstBuffer *buffer)
{
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GstVaapiDecoderStatus status;
    gboolean is_eos;
    guchar *buf;
    guint buf_size, size;
    guint32 start_code;
    gint ofs;

    buf      = GST_BUFFER_DATA(buffer);
    buf_size = GST_BUFFER_SIZE(buffer);
    is_eos   = GST_BUFFER_IS_EOS(buffer);
    if (buf && buf_size > 0)
        gst_adapter_push(priv->adapter, gst_buffer_ref(buffer));

    size = gst_adapter_available(priv->adapter);
    do {
        if (size == 0) {
            status = GST_VAAPI_DECODER_STATUS_SUCCESS;
            break;
        }

        status = GST_VAAPI_DECODER_STATUS_ERROR_NO_DATA;
        if (size < 4)
            break;
        ofs = scan_for_start_code(priv->adapter, 0, size, &start_code);
        if (ofs < 0)
            break;
        gst_adapter_flush(priv->adapter, ofs);
        size -= ofs;

        status = gst_vaapi_decoder_check_status(GST_VAAPI_DECODER(decoder));
        if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
            break;

        status = GST_VAAPI_DECODER_STATUS_ERROR_NO_DATA;
        if (size < 8)
            break;
        ofs = scan_for_start_code(priv->adapter, 4, size - 4, NULL);
        if (ofs < 0) {
            // Assume the whole packet is present if end-of-stream
            if (!is_eos)
                break;
            ofs = size;
        }
        buffer = gst_adapter_take_buffer(priv->adapter, ofs);
        size -= ofs;

        buf      = GST_BUFFER_DATA(buffer);
        buf_size = GST_BUFFER_SIZE(buffer);
        status   = decode_packet(decoder, buf, buf_size);

        gst_buffer_unref(buffer);
    } while (status == GST_VAAPI_DECODER_STATUS_SUCCESS);

    if (is_eos && (status == GST_VAAPI_DECODER_STATUS_SUCCESS ||
                   status == GST_VAAPI_DECODER_STATUS_ERROR_NO_DATA))
        status = decode_sequence_end(decoder);
    return status;
}

GstVaapiDecoderStatus
gst_vaapi_decoder_mpeg2_decode(GstVaapiDecoder *base, GstBuffer *buffer)
{
    GstVaapiDecoderMpeg2 * const decoder = GST_VAAPI_DECODER_MPEG2(base);
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;

    g_return_val_if_fail(priv->is_constructed,
                         GST_VAAPI_DECODER_STATUS_ERROR_INIT_FAILED);

    if (!priv->is_opened) {
        priv->is_opened = gst_vaapi_decoder_mpeg2_open(decoder, buffer);
        if (!priv->is_opened)
            return GST_VAAPI_DECODER_STATUS_ERROR_UNSUPPORTED_CODEC;
    }
    return decode_buffer(decoder, buffer);
}

static void
gst_vaapi_decoder_mpeg2_finalize(GObject *object)
{
    GstVaapiDecoderMpeg2 * const decoder = GST_VAAPI_DECODER_MPEG2(object);

    gst_vaapi_decoder_mpeg2_destroy(decoder);

    G_OBJECT_CLASS(gst_vaapi_decoder_mpeg2_parent_class)->finalize(object);
}

static void
gst_vaapi_decoder_mpeg2_constructed(GObject *object)
{
    GstVaapiDecoderMpeg2 * const decoder = GST_VAAPI_DECODER_MPEG2(object);
    GstVaapiDecoderMpeg2Private * const priv = decoder->priv;
    GObjectClass *parent_class;

    parent_class = G_OBJECT_CLASS(gst_vaapi_decoder_mpeg2_parent_class);
    if (parent_class->constructed)
        parent_class->constructed(object);

    priv->is_constructed = gst_vaapi_decoder_mpeg2_create(decoder);
}

static void
gst_vaapi_decoder_mpeg2_class_init(GstVaapiDecoderMpeg2Class *klass)
{
    GObjectClass * const object_class = G_OBJECT_CLASS(klass);
    GstVaapiDecoderClass * const decoder_class = GST_VAAPI_DECODER_CLASS(klass);

    g_type_class_add_private(klass, sizeof(GstVaapiDecoderMpeg2Private));

    object_class->finalize      = gst_vaapi_decoder_mpeg2_finalize;
    object_class->constructed   = gst_vaapi_decoder_mpeg2_constructed;

    decoder_class->decode       = gst_vaapi_decoder_mpeg2_decode;
}

static void
gst_vaapi_decoder_mpeg2_init(GstVaapiDecoderMpeg2 *decoder)
{
    GstVaapiDecoderMpeg2Private *priv;

    priv                        = GST_VAAPI_DECODER_MPEG2_GET_PRIVATE(decoder);
    decoder->priv               = priv;
    priv->width                 = 0;
    priv->height                = 0;
    priv->fps_n                 = 0;
    priv->fps_d                 = 0;
    priv->hw_profile            = GST_VAAPI_PROFILE_UNKNOWN;
    priv->profile               = GST_VAAPI_PROFILE_MPEG2_SIMPLE;
    priv->current_picture       = NULL;
    priv->adapter               = NULL;
    priv->is_constructed        = FALSE;
    priv->is_opened             = FALSE;
    priv->has_seq_ext           = FALSE;
    priv->has_seq_scalable_ext  = FALSE;
    priv->has_pic_ext           = FALSE;
    priv->has_quant_matrix_ext  = FALSE;
    priv->size_changed          = FALSE;
    priv->profile_changed       = TRUE; /* Allow fallbacks to work */
    priv->quant_matrix_changed  = FALSE;
    priv->progressive_sequence  = FALSE;
    priv->closed_gop            = FALSE;
    priv->broken_link           = FALSE;
}

/**
 * gst_vaapi_decoder_mpeg2_new:
 * @display: a #GstVaapiDisplay
 * @caps: a #GstCaps holding codec information
 *
 * Creates a new #GstVaapiDecoder for MPEG-2 decoding.  The @caps can
 * hold extra information like codec-data and pictured coded size.
 *
 * Return value: the newly allocated #GstVaapiDecoder object
 */
GstVaapiDecoder *
gst_vaapi_decoder_mpeg2_new(GstVaapiDisplay *display, GstCaps *caps)
{
    GstVaapiDecoderMpeg2 *decoder;

    g_return_val_if_fail(GST_VAAPI_IS_DISPLAY(display), NULL);
    g_return_val_if_fail(GST_IS_CAPS(caps), NULL);

    decoder = g_object_new(
        GST_VAAPI_TYPE_DECODER_MPEG2,
        "display",      display,
        "caps",         caps,
        NULL
    );
    if (!decoder->priv->is_constructed) {
        g_object_unref(decoder);
        return NULL;
    }
    return GST_VAAPI_DECODER_CAST(decoder);
}