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avcodec/mpeg4video: Skip unneeded element when parsing picture header

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Namely, skip some elements that are only useful for a decoder
when calling ff_mpeg4_decode_picture_header() from the MPEG-4 parser.

In particular, this ensures that the VLCs need no longer be
initialized by the parser.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-01-04 06:05:59 +01:00
parent 6739bb5a0e
commit f0194e860e
4 changed files with 21 additions and 8 deletions
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4
libavcodec/h263dec.c
View File

@ -507,9 +507,9 @@ retry:
GetBitContext gb;
if (init_get_bits8(&gb, s->avctx->extradata, s->avctx->extradata_size) >= 0 )
ff_mpeg4_decode_picture_header(avctx->priv_data, &gb, 1);
ff_mpeg4_decode_picture_header(avctx->priv_data, &gb, 1, 0);
}
ret = ff_mpeg4_decode_picture_header(avctx->priv_data, &s->gb, 0);
ret = ff_mpeg4_decode_picture_header(avctx->priv_data, &s->gb, 0, 0);
} else if (CONFIG_H263I_DECODER && s->codec_id == AV_CODEC_ID_H263I) {
ret = ff_intel_h263_decode_picture_header(s);
} else if (CONFIG_FLV_DECODER && s->h263_flv) {

3
libavcodec/mpeg4video.h
View File

@ -160,7 +160,8 @@ void ff_mpeg4_pred_ac(MpegEncContext *s, int16_t *block, int n,
void ff_set_mpeg4_time(MpegEncContext *s);
int ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number);
int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb, int header);
int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb,
int header, int parse_only);
void ff_mpeg4_encode_video_packet_header(MpegEncContext *s);
void ff_mpeg4_clean_buffers(MpegEncContext *s);
void ff_mpeg4_stuffing(PutBitContext *pbc);

4
libavcodec/mpeg4video_parser.c
View File

@ -100,13 +100,13 @@ static int mpeg4_decode_header(AVCodecParserContext *s1, AVCodecContext *avctx,
if (avctx->extradata_size && pc->first_picture) {
init_get_bits(gb, avctx->extradata, avctx->extradata_size * 8);
ret = ff_mpeg4_decode_picture_header(dec_ctx, gb, 1);
ret = ff_mpeg4_decode_picture_header(dec_ctx, gb, 1, 1);
if (ret < 0)
av_log(avctx, AV_LOG_WARNING, "Failed to parse extradata\n");
}
init_get_bits(gb, buf, 8 * buf_size);
ret = ff_mpeg4_decode_picture_header(dec_ctx, gb, 0);
ret = ff_mpeg4_decode_picture_header(dec_ctx, gb, 0, 1);
if (s->width && (!avctx->width || !avctx->height ||
!avctx->coded_width || !avctx->coded_height)) {
ret = ff_set_dimensions(avctx, s->width, s->height);

18
libavcodec/mpeg4videodec.c
View File

@ -2844,7 +2844,8 @@ int ff_mpeg4_workaround_bugs(AVCodecContext *avctx)
return 0;
}
static int decode_vop_header(Mpeg4DecContext *ctx, GetBitContext *gb)
static int decode_vop_header(Mpeg4DecContext *ctx, GetBitContext *gb,
int parse_only)
{
MpegEncContext *s = &ctx->m;
int time_incr, time_increment;
@ -3018,6 +3019,12 @@ static int decode_vop_header(Mpeg4DecContext *ctx, GetBitContext *gb)
ff_init_scantable(s->idsp.idct_permutation, &s->intra_v_scantable, ff_alternate_vertical_scan);
}
/* Skip at this point when only parsing since the remaining
* data is not useful for a parser and requires the
* sprite_trajectory VLC to be initialized. */
if (parse_only)
goto end;
if (s->pict_type == AV_PICTURE_TYPE_S) {
if((ctx->vol_sprite_usage == STATIC_SPRITE ||
ctx->vol_sprite_usage == GMC_SPRITE)) {
@ -3095,6 +3102,8 @@ static int decode_vop_header(Mpeg4DecContext *ctx, GetBitContext *gb)
skip_bits(gb, 2); // ref_select_code
}
}
end:
/* detect buggy encoders which don't set the low_delay flag
* (divx4/xvid/opendivx). Note we cannot detect divx5 without B-frames
* easily (although it's buggy too) */
@ -3214,11 +3223,14 @@ static int decode_studiovisualobject(Mpeg4DecContext *ctx, GetBitContext *gb)
* Decode MPEG-4 headers.
*
* @param header If set the absence of a VOP is not treated as error; otherwise, it is treated as such.
* @param parse_only If set, things only relevant to a decoder may be skipped;
* furthermore, the VLC tables may be uninitialized.
* @return <0 if an error occurred
* FRAME_SKIPPED if a not coded VOP is found
* 0 else
*/
int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb, int header)
int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb,
int header, int parse_only)
{
MpegEncContext *s = &ctx->m;
unsigned startcode, v;
@ -3371,7 +3383,7 @@ end:
}
return decode_studio_vop_header(ctx, gb);
} else
return decode_vop_header(ctx, gb);
return decode_vop_header(ctx, gb, parse_only);
}
av_cold void ff_mpeg4videodec_static_init(void) {