[FFmpeg-devel] [PATCH 2/4] avcodec/h264_slice: compute and export film grain seed
Niklas Haas
ffmpeg at haasn.xyz
Sat Aug 14 14:36:18 EEST 2021
From: Niklas Haas <git at haasn.dev>
>From SMPTE RDD 5-2006, the grain seed is to be computed from the
following definition of `pic_offset`:
> When decoding H.264 | MPEG-4 AVC bitstreams, pic_offset is defined as
> follows:
> - pic_offset = PicOrderCnt(CurrPic) + (PicOrderCnt_offset << 5)
> where:
> - PicOrderCnt(CurrPic) is the picture order count of the current frame,
> which shall be derived from [the video stream].
>
> - PicOrderCnt_offset is set to idr_pic_id on IDR frames. idr_pic_id
> shall be read from the slice header of [the video stream]. On non-IDR I
> frames, PicOrderCnt_offset is set to 0. A frame shall be classified as I
> frame when all its slices are I slices, which may be optionally
> designated by setting primary_pic_type to 0 in the access delimiter NAL
> unit. Otherwise, PicOrderCnt_offset it not changed. PicOrderCnt_offset is
> updated in decoding order.
To forward this information correctly, we need to make a number of
annoying changes to h264_slice:
- We need to keep track of the `PicOrderCnt_offset`, and update it to
the decoded value of `idr_pic_id` on IDR frames.
- We need to keep track of whether or not a frame contained any non-I
slices, so we can detect the "non-IDR I frame" condition, and reset
`PicOrderCnt_offset` back to 0. This is *not* synonymous with existing
fields such as `pic->f->pict_type` because that is somehow only set
based on the first slice in a frame, so we introduce a new field
`picture_intra_only` which is set to 0 when decoding any non-I slice.
- We need to compute this derived `pic_offset` at the *end* of the
frame, rather than at the beginning (where the SEI is decoded/set),
because it now depends on the types of the slices present in the same
frame.
If there's a less ugly way to accomplish the above, I don't see it.
Suggestions welcome(tm).
Signed-off-by: Niklas Haas <git at haasn.dev>
---
libavcodec/h264_picture.c | 13 ++++++++++++-
libavcodec/h264_slice.c | 11 ++++++++++-
libavcodec/h264dec.h | 7 +++++++
libavutil/film_grain_params.h | 3 +++
4 files changed, 32 insertions(+), 2 deletions(-)
diff --git a/libavcodec/h264_picture.c b/libavcodec/h264_picture.c
index ff30166b4d..b79944b794 100644
--- a/libavcodec/h264_picture.c
+++ b/libavcodec/h264_picture.c
@@ -27,6 +27,7 @@
#include "libavutil/avassert.h"
#include "libavutil/imgutils.h"
+#include "libavutil/film_grain_params.h"
#include "internal.h"
#include "cabac.h"
#include "cabac_functions.h"
@@ -212,6 +213,8 @@ void ff_h264_set_erpic(ERPicture *dst, H264Picture *src)
int ff_h264_field_end(H264Context *h, H264SliceContext *sl, int in_setup)
{
AVCodecContext *const avctx = h->avctx;
+ H264Picture *cur = h->cur_pic_ptr;
+ AVFrameSideData *sd;
int err = 0;
h->mb_y = 0;
@@ -225,6 +228,9 @@ int ff_h264_field_end(H264Context *h, H264SliceContext *sl, int in_setup)
h->poc.prev_frame_num = h->poc.frame_num;
}
+ if (!h->picture_idr && h->picture_intra_only)
+ h->poc_offset = 0;
+
if (avctx->hwaccel) {
err = avctx->hwaccel->end_frame(avctx);
if (err < 0)
@@ -232,8 +238,13 @@ int ff_h264_field_end(H264Context *h, H264SliceContext *sl, int in_setup)
"hardware accelerator failed to decode picture\n");
}
+ if ((sd = av_frame_get_side_data(cur->f, AV_FRAME_DATA_FILM_GRAIN_PARAMS))) {
+ AVFilmGrainParams *fgp = (AVFilmGrainParams *) sd->data;
+ fgp->seed = cur->poc + (h->poc_offset << 5);
+ }
+
if (!in_setup && !h->droppable)
- ff_thread_report_progress(&h->cur_pic_ptr->tf, INT_MAX,
+ ff_thread_report_progress(&cur->tf, INT_MAX,
h->picture_structure == PICT_BOTTOM_FIELD);
emms_c();
diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index 0d7107d455..65d0259a71 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -406,6 +406,7 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
h->next_output_pic = h1->next_output_pic;
h->next_outputed_poc = h1->next_outputed_poc;
+ h->poc_offset = h1->poc_offset;
memcpy(h->mmco, h1->mmco, sizeof(h->mmco));
h->nb_mmco = h1->nb_mmco;
@@ -510,6 +511,7 @@ static int h264_frame_start(H264Context *h)
pic->sei_recovery_frame_cnt = h->sei.recovery_point.recovery_frame_cnt;
pic->f->pict_type = h->slice_ctx[0].slice_type;
+ h->picture_intra_only = 1; // set to 0 by h264_slice_init
pic->f->crop_left = h->crop_left;
pic->f->crop_right = h->crop_right;
@@ -1335,6 +1337,7 @@ static int h264_export_frame_props(H264Context *h)
return AVERROR(ENOMEM);
fgp->type = AV_FILM_GRAIN_PARAMS_H274;
+ /* fgp->seed is set by ff_h264_field_end */
fgp->codec.h274.model_id = fgc->model_id;
if (fgc->separate_colour_description_present_flag) {
@@ -1543,6 +1546,9 @@ static int h264_field_start(H264Context *h, const H264SliceContext *sl,
h->poc.delta_poc[0] = sl->delta_poc[0];
h->poc.delta_poc[1] = sl->delta_poc[1];
+ if (nal->type == H264_NAL_IDR_SLICE)
+ h->poc_offset = sl->idr_pic_id;
+
/* Shorten frame num gaps so we don't have to allocate reference
* frames just to throw them away */
if (h->poc.frame_num != h->poc.prev_frame_num) {
@@ -1891,7 +1897,7 @@ static int h264_slice_header_parse(const H264Context *h, H264SliceContext *sl,
}
if (nal->type == H264_NAL_IDR_SLICE)
- get_ue_golomb_long(&sl->gb); /* idr_pic_id */
+ sl->idr_pic_id = get_ue_golomb_long(&sl->gb);
sl->poc_lsb = 0;
sl->delta_poc_bottom = 0;
@@ -2024,6 +2030,9 @@ static int h264_slice_init(H264Context *h, H264SliceContext *sl,
return AVERROR_INVALIDDATA;
}
+ if (sl->slice_type_nos != AV_PICTURE_TYPE_I)
+ h->picture_intra_only = 0;
+
av_assert1(h->mb_num == h->mb_width * h->mb_height);
if (sl->first_mb_addr << FIELD_OR_MBAFF_PICTURE(h) >= h->mb_num ||
sl->first_mb_addr >= h->mb_num) {
diff --git a/libavcodec/h264dec.h b/libavcodec/h264dec.h
index 125966aa04..7c419de051 100644
--- a/libavcodec/h264dec.h
+++ b/libavcodec/h264dec.h
@@ -331,6 +331,7 @@ typedef struct H264SliceContext {
int explicit_ref_marking;
int frame_num;
+ int idr_pic_id;
int poc_lsb;
int delta_poc_bottom;
int delta_poc[2];
@@ -384,6 +385,11 @@ typedef struct H264Context {
*/
int picture_idr;
+ /*
+ * Set to 1 when the current picture contains only I slices, 0 otherwise.
+ */
+ int picture_intra_only;
+
int crop_left;
int crop_right;
int crop_top;
@@ -473,6 +479,7 @@ typedef struct H264Context {
int last_pocs[MAX_DELAYED_PIC_COUNT];
H264Picture *next_output_pic;
int next_outputed_poc;
+ int poc_offset; ///< PicOrderCnt_offset from SMPTE RDD-2006
/**
* memory management control operations buffer.
diff --git a/libavutil/film_grain_params.h b/libavutil/film_grain_params.h
index 7350dfc5b8..f3bd0a4a6a 100644
--- a/libavutil/film_grain_params.h
+++ b/libavutil/film_grain_params.h
@@ -221,6 +221,9 @@ typedef struct AVFilmGrainParams {
/**
* Seed to use for the synthesis process, if the codec allows for it.
+ *
+ * @note For H.264, this refers to `pic_offset` as defined in
+ * SMPTE RDD 5-2006.
*/
uint64_t seed;
--
2.32.0
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