FFmpeg-devel-v2-7-8-avcodec-Add-V4L2-Request-API-h264-hwaccel.patch

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From: Jonas Karlman <jonas@kwiboo.se>
To: ffmpeg-devel@ffmpeg.org
Date: Tue,  6 Aug 2024 09:06:06 +0000
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Subject: [FFmpeg-devel] [PATCH v2 7/8] avcodec: Add V4L2 Request API h264
 hwaccel
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Cc: Benjamin Gaignard <benjamin.gaignard@collabora.com>,
 Jonas Karlman <jonas@kwiboo.se>, Alex Bee <knaerzche@gmail.com>,
 Jernej Skrabec <jernej.skrabec@gmail.com>,
 Boris Brezillon <boris.brezillon@collabora.com>,
 Nicolas Dufresne <nicolas.dufresne@collabora.com>
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From: Jernej Skrabec <jernej.skrabec@gmail.com>

Add a V4L2 Request API hwaccel for H.264, supporting both slice and
frame decoding modes.

Support for H.264 is enabled when Linux kernel headers declare the
control id V4L2_CID_STATELESS_H264_DECODE_MODE, added in v5.11.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Co-developed-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
---
In a future revision or follow up patch a check for PROFILE and LEVEL
controls should be added to filter out any video device not reporting
support for current profile and level.
---
 configure                      |   3 +
 libavcodec/Makefile            |   1 +
 libavcodec/h264_slice.c        |   7 +
 libavcodec/h264dec.c           |   3 +
 libavcodec/hwaccels.h          |   1 +
 libavcodec/v4l2_request_h264.c | 523 +++++++++++++++++++++++++++++++++
 6 files changed, 538 insertions(+)
 create mode 100644 libavcodec/v4l2_request_h264.c

diff --git a/configure b/configure
index 35e33a8409..0dcd834e08 100755
--- a/configure
+++ b/configure
@@ -3188,6 +3188,8 @@ h264_dxva2_hwaccel_deps="dxva2"
 h264_dxva2_hwaccel_select="h264_decoder"
 h264_nvdec_hwaccel_deps="nvdec"
 h264_nvdec_hwaccel_select="h264_decoder"
+h264_v4l2request_hwaccel_deps="v4l2_request h264_v4l2_request"
+h264_v4l2request_hwaccel_select="h264_decoder"
 h264_vaapi_hwaccel_deps="vaapi"
 h264_vaapi_hwaccel_select="h264_decoder"
 h264_vdpau_hwaccel_deps="vdpau"
@@ -7179,6 +7181,7 @@ if enabled v4l2_m2m; then
 fi
 
 if enabled v4l2_request; then
+    check_cc h264_v4l2_request linux/videodev2.h "int i = V4L2_CID_STATELESS_H264_DECODE_MODE"
     check_cc mpeg2_v4l2_request linux/videodev2.h "int i = V4L2_CID_STATELESS_MPEG2_SEQUENCE"
     check_cc v4l2_m2m_hold_capture_buf linux/videodev2.h "int i = V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF"
     check_func_headers "linux/media.h linux/videodev2.h" v4l2_timeval_to_ns
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 5c51818d0d..dadddb55a8 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -1009,6 +1009,7 @@ OBJS-$(CONFIG_H264_DXVA2_HWACCEL)         += dxva2_h264.o
 OBJS-$(CONFIG_H264_D3D12VA_HWACCEL)       += dxva2_h264.o d3d12va_h264.o
 OBJS-$(CONFIG_H264_NVDEC_HWACCEL)         += nvdec_h264.o
 OBJS-$(CONFIG_H264_QSV_HWACCEL)           += qsvdec.o
+OBJS-$(CONFIG_H264_V4L2REQUEST_HWACCEL)   += v4l2_request_h264.o
 OBJS-$(CONFIG_H264_VAAPI_HWACCEL)         += vaapi_h264.o
 OBJS-$(CONFIG_H264_VDPAU_HWACCEL)         += vdpau_h264.o
 OBJS-$(CONFIG_H264_VIDEOTOOLBOX_HWACCEL)  += videotoolbox.o
diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index 58a48f3fbe..259a2c307a 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -781,6 +781,7 @@ static enum AVPixelFormat get_pixel_format(H264Context *h, int force_callback)
                      (CONFIG_H264_D3D11VA_HWACCEL * 2) + \
                      CONFIG_H264_D3D12VA_HWACCEL + \
                      CONFIG_H264_NVDEC_HWACCEL + \
+                     CONFIG_H264_V4L2REQUEST_HWACCEL + \
                      CONFIG_H264_VAAPI_HWACCEL + \
                      CONFIG_H264_VIDEOTOOLBOX_HWACCEL + \
                      CONFIG_H264_VDPAU_HWACCEL + \
@@ -806,6 +807,9 @@ static enum AVPixelFormat get_pixel_format(H264Context *h, int force_callback)
 #endif
 #if CONFIG_H264_VULKAN_HWACCEL
         *fmt++ = AV_PIX_FMT_VULKAN;
+#endif
+#if CONFIG_H264_V4L2REQUEST_HWACCEL
+        *fmt++ = AV_PIX_FMT_DRM_PRIME;
 #endif
         if (CHROMA444(h)) {
             if (h->avctx->colorspace == AVCOL_SPC_RGB) {
@@ -862,6 +866,9 @@ static enum AVPixelFormat get_pixel_format(H264Context *h, int force_callback)
 #if CONFIG_H264_VIDEOTOOLBOX_HWACCEL
         if (h->avctx->colorspace != AVCOL_SPC_RGB)
             *fmt++ = AV_PIX_FMT_VIDEOTOOLBOX;
+#endif
+#if CONFIG_H264_V4L2REQUEST_HWACCEL
+        *fmt++ = AV_PIX_FMT_DRM_PRIME;
 #endif
         if (CHROMA444(h)) {
             if (h->avctx->colorspace == AVCOL_SPC_RGB)
diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index c77d8f42db..7a274c3264 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -1160,6 +1160,9 @@ const FFCodec ff_h264_decoder = {
 #endif
 #if CONFIG_H264_VULKAN_HWACCEL
                                HWACCEL_VULKAN(h264),
+#endif
+#if CONFIG_H264_V4L2REQUEST_HWACCEL
+                               HWACCEL_V4L2REQUEST(h264),
 #endif
                                NULL
                            },
diff --git a/libavcodec/hwaccels.h b/libavcodec/hwaccels.h
index 0cba7c71be..024e021d73 100644
--- a/libavcodec/hwaccels.h
+++ b/libavcodec/hwaccels.h
@@ -34,6 +34,7 @@ extern const struct FFHWAccel ff_h264_d3d11va2_hwaccel;
 extern const struct FFHWAccel ff_h264_d3d12va_hwaccel;
 extern const struct FFHWAccel ff_h264_dxva2_hwaccel;
 extern const struct FFHWAccel ff_h264_nvdec_hwaccel;
+extern const struct FFHWAccel ff_h264_v4l2request_hwaccel;
 extern const struct FFHWAccel ff_h264_vaapi_hwaccel;
 extern const struct FFHWAccel ff_h264_vdpau_hwaccel;
 extern const struct FFHWAccel ff_h264_videotoolbox_hwaccel;
diff --git a/libavcodec/v4l2_request_h264.c b/libavcodec/v4l2_request_h264.c
new file mode 100644
index 0000000000..57651282ce
--- /dev/null
+++ b/libavcodec/v4l2_request_h264.c
@@ -0,0 +1,523 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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.
+ *
+ * FFmpeg 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 FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "config.h"
+
+#include "h264dec.h"
+#include "hwaccel_internal.h"
+#include "hwconfig.h"
+#include "internal.h"
+#include "v4l2_request.h"
+
+typedef struct V4L2RequestContextH264 {
+    V4L2RequestContext base;
+    enum v4l2_stateless_h264_decode_mode decode_mode;
+    enum v4l2_stateless_h264_start_code start_code;
+} V4L2RequestContextH264;
+
+typedef struct V4L2RequestControlsH264 {
+    V4L2RequestPictureContext pic;
+    struct v4l2_ctrl_h264_sps sps;
+    struct v4l2_ctrl_h264_pps pps;
+    struct v4l2_ctrl_h264_scaling_matrix scaling_matrix;
+    struct v4l2_ctrl_h264_decode_params decode_params;
+    struct v4l2_ctrl_h264_slice_params slice_params;
+    struct v4l2_ctrl_h264_pred_weights pred_weights;
+    bool pred_weights_required;
+    bool first_slice;
+    int num_slices;
+} V4L2RequestControlsH264;
+
+static uint8_t nalu_slice_start_code[] = { 0x00, 0x00, 0x01 };
+
+static void fill_weight_factors(struct v4l2_h264_weight_factors *weight_factors,
+                                int list, const H264SliceContext *sl)
+{
+    for (int i = 0; i < sl->ref_count[list]; i++) {
+        if (sl->pwt.luma_weight_flag[list]) {
+            weight_factors->luma_weight[i] = sl->pwt.luma_weight[i][list][0];
+            weight_factors->luma_offset[i] = sl->pwt.luma_weight[i][list][1];
+        } else {
+            weight_factors->luma_weight[i] = 1 << sl->pwt.luma_log2_weight_denom;
+            weight_factors->luma_offset[i] = 0;
+        }
+        for (int j = 0; j < 2; j++) {
+            if (sl->pwt.chroma_weight_flag[list]) {
+                weight_factors->chroma_weight[i][j] = sl->pwt.chroma_weight[i][list][j][0];
+                weight_factors->chroma_offset[i][j] = sl->pwt.chroma_weight[i][list][j][1];
+            } else {
+                weight_factors->chroma_weight[i][j] = 1 << sl->pwt.chroma_log2_weight_denom;
+                weight_factors->chroma_offset[i][j] = 0;
+            }
+        }
+    }
+}
+
+static void fill_dpb_entry(struct v4l2_h264_dpb_entry *entry,
+                           const H264Picture *pic, int long_idx)
+{
+    entry->reference_ts = ff_v4l2_request_get_capture_timestamp(pic->f);
+    entry->pic_num = pic->pic_id;
+    entry->frame_num = pic->long_ref ? long_idx : pic->frame_num;
+    entry->fields = pic->reference & V4L2_H264_FRAME_REF;
+    entry->flags = V4L2_H264_DPB_ENTRY_FLAG_VALID;
+    if (entry->fields)
+        entry->flags |= V4L2_H264_DPB_ENTRY_FLAG_ACTIVE;
+    if (pic->long_ref)
+        entry->flags |= V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM;
+    if (pic->field_picture)
+        entry->flags |= V4L2_H264_DPB_ENTRY_FLAG_FIELD;
+    if (pic->field_poc[0] != INT_MAX)
+        entry->top_field_order_cnt = pic->field_poc[0];
+    if (pic->field_poc[1] != INT_MAX)
+        entry->bottom_field_order_cnt = pic->field_poc[1];
+}
+
+static void fill_dpb(struct v4l2_ctrl_h264_decode_params *decode_params,
+                     const H264Context *h)
+{
+    int entries = 0;
+
+    for (int i = 0; i < h->short_ref_count; i++) {
+        const H264Picture *pic = h->short_ref[i];
+        if (pic && (pic->field_poc[0] != INT_MAX || pic->field_poc[1] != INT_MAX))
+            fill_dpb_entry(&decode_params->dpb[entries++], pic, pic->pic_id);
+    }
+
+    if (!h->long_ref_count)
+        return;
+
+    for (int i = 0; i < FF_ARRAY_ELEMS(h->long_ref); i++) {
+        const H264Picture *pic = h->long_ref[i];
+        if (pic && (pic->field_poc[0] != INT_MAX || pic->field_poc[1] != INT_MAX))
+            fill_dpb_entry(&decode_params->dpb[entries++], pic, i);
+    }
+}
+
+static void fill_ref_list(struct v4l2_h264_reference *reference,
+                          struct v4l2_ctrl_h264_decode_params *decode_params,
+                          const H264Ref *ref)
+{
+    uint64_t timestamp;
+
+    if (!ref->parent)
+        return;
+
+    timestamp = ff_v4l2_request_get_capture_timestamp(ref->parent->f);
+
+    for (uint8_t i = 0; i < FF_ARRAY_ELEMS(decode_params->dpb); i++) {
+        struct v4l2_h264_dpb_entry *entry = &decode_params->dpb[i];
+        if ((entry->flags & V4L2_H264_DPB_ENTRY_FLAG_VALID) &&
+            entry->reference_ts == timestamp) {
+            reference->fields = ref->reference & V4L2_H264_FRAME_REF;
+            reference->index = i;
+            return;
+        }
+    }
+}
+
+static void fill_sps(struct v4l2_ctrl_h264_sps *ctrl, const H264Context *h)
+{
+    const SPS *sps = h->ps.sps;
+
+    *ctrl = (struct v4l2_ctrl_h264_sps) {
+        .profile_idc = sps->profile_idc,
+        .constraint_set_flags = sps->constraint_set_flags,
+        .level_idc = sps->level_idc,
+        .seq_parameter_set_id = sps->sps_id,
+        .chroma_format_idc = sps->chroma_format_idc,
+        .bit_depth_luma_minus8 = sps->bit_depth_luma - 8,
+        .bit_depth_chroma_minus8 = sps->bit_depth_chroma - 8,
+        .log2_max_frame_num_minus4 = sps->log2_max_frame_num - 4,
+        .pic_order_cnt_type = sps->poc_type,
+        .log2_max_pic_order_cnt_lsb_minus4 = sps->log2_max_poc_lsb - 4,
+        .max_num_ref_frames = sps->ref_frame_count,
+        .num_ref_frames_in_pic_order_cnt_cycle = sps->poc_cycle_length,
+        .offset_for_non_ref_pic = sps->offset_for_non_ref_pic,
+        .offset_for_top_to_bottom_field = sps->offset_for_top_to_bottom_field,
+        .pic_width_in_mbs_minus1 = h->mb_width - 1,
+        .pic_height_in_map_units_minus1 = sps->frame_mbs_only_flag ?
+                                          h->mb_height - 1 : h->mb_height / 2 - 1,
+    };
+
+    if (sps->poc_cycle_length > 0 && sps->poc_cycle_length <= 255)
+        memcpy(ctrl->offset_for_ref_frame, sps->offset_for_ref_frame,
+               sps->poc_cycle_length * sizeof(ctrl->offset_for_ref_frame[0]));
+
+    if (sps->residual_color_transform_flag)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_SEPARATE_COLOUR_PLANE;
+
+    if (sps->transform_bypass)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_QPPRIME_Y_ZERO_TRANSFORM_BYPASS;
+
+    if (sps->delta_pic_order_always_zero_flag)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_DELTA_PIC_ORDER_ALWAYS_ZERO;
+
+    if (sps->gaps_in_frame_num_allowed_flag)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_GAPS_IN_FRAME_NUM_VALUE_ALLOWED;
+
+    if (sps->frame_mbs_only_flag)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY;
+
+    if (sps->mb_aff)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_MB_ADAPTIVE_FRAME_FIELD;
+
+    if (sps->direct_8x8_inference_flag)
+        ctrl->flags |= V4L2_H264_SPS_FLAG_DIRECT_8X8_INFERENCE;
+}
+
+static void fill_pps(struct v4l2_ctrl_h264_pps *ctrl, const H264Context *h)
+{
+    const SPS *sps = h->ps.sps;
+    const PPS *pps = h->ps.pps;
+    const H264SliceContext *sl = &h->slice_ctx[0];
+    int qp_bd_offset = 6 * (sps->bit_depth_luma - 8);
+
+    *ctrl = (struct v4l2_ctrl_h264_pps) {
+        .pic_parameter_set_id = sl->pps_id,
+        .seq_parameter_set_id = pps->sps_id,
+        .num_slice_groups_minus1 = pps->slice_group_count - 1,
+        .num_ref_idx_l0_default_active_minus1 = pps->ref_count[0] - 1,
+        .num_ref_idx_l1_default_active_minus1 = pps->ref_count[1] - 1,
+        .weighted_bipred_idc = pps->weighted_bipred_idc,
+        .pic_init_qp_minus26 = pps->init_qp - 26 - qp_bd_offset,
+        .pic_init_qs_minus26 = pps->init_qs - 26 - qp_bd_offset,
+        .chroma_qp_index_offset = pps->chroma_qp_index_offset[0],
+        .second_chroma_qp_index_offset = pps->chroma_qp_index_offset[1],
+    };
+
+    if (pps->cabac)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_ENTROPY_CODING_MODE;
+
+    if (pps->pic_order_present)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_BOTTOM_FIELD_PIC_ORDER_IN_FRAME_PRESENT;
+
+    if (pps->weighted_pred)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_WEIGHTED_PRED;
+
+    if (pps->deblocking_filter_parameters_present)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_DEBLOCKING_FILTER_CONTROL_PRESENT;
+
+    if (pps->constrained_intra_pred)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_CONSTRAINED_INTRA_PRED;
+
+    if (pps->redundant_pic_cnt_present)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_REDUNDANT_PIC_CNT_PRESENT;
+
+    if (pps->transform_8x8_mode)
+        ctrl->flags |= V4L2_H264_PPS_FLAG_TRANSFORM_8X8_MODE;
+
+    /* FFmpeg always provide a scaling matrix */
+    ctrl->flags |= V4L2_H264_PPS_FLAG_SCALING_MATRIX_PRESENT;
+}
+
+static int v4l2_request_h264_start_frame(AVCodecContext *avctx,
+                                         av_unused const uint8_t *buffer,
+                                         av_unused uint32_t size)
+{
+    const H264Context *h = avctx->priv_data;
+    const PPS *pps = h->ps.pps;
+    const SPS *sps = h->ps.sps;
+    const H264SliceContext *sl = &h->slice_ctx[0];
+    V4L2RequestControlsH264 *controls = h->cur_pic_ptr->hwaccel_picture_private;
+    int ret;
+
+    ret = ff_v4l2_request_start_frame(avctx, &controls->pic, h->cur_pic_ptr->f);
+    if (ret)
+        return ret;
+
+    fill_sps(&controls->sps, h);
+    fill_pps(&controls->pps, h);
+
+    memcpy(controls->scaling_matrix.scaling_list_4x4, pps->scaling_matrix4,
+           sizeof(controls->scaling_matrix.scaling_list_4x4));
+    memcpy(controls->scaling_matrix.scaling_list_8x8[0], pps->scaling_matrix8[0],
+           sizeof(controls->scaling_matrix.scaling_list_8x8[0]));
+    memcpy(controls->scaling_matrix.scaling_list_8x8[1], pps->scaling_matrix8[3],
+           sizeof(controls->scaling_matrix.scaling_list_8x8[1]));
+
+    if (sps->chroma_format_idc == 3) {
+        memcpy(controls->scaling_matrix.scaling_list_8x8[2], pps->scaling_matrix8[1],
+               sizeof(controls->scaling_matrix.scaling_list_8x8[2]));
+        memcpy(controls->scaling_matrix.scaling_list_8x8[3], pps->scaling_matrix8[4],
+               sizeof(controls->scaling_matrix.scaling_list_8x8[3]));
+        memcpy(controls->scaling_matrix.scaling_list_8x8[4], pps->scaling_matrix8[2],
+               sizeof(controls->scaling_matrix.scaling_list_8x8[4]));
+        memcpy(controls->scaling_matrix.scaling_list_8x8[5], pps->scaling_matrix8[5],
+               sizeof(controls->scaling_matrix.scaling_list_8x8[5]));
+    }
+
+    controls->decode_params = (struct v4l2_ctrl_h264_decode_params) {
+        .nal_ref_idc = h->nal_ref_idc,
+        .frame_num = h->poc.frame_num,
+        .top_field_order_cnt = h->cur_pic_ptr->field_poc[0] != INT_MAX ?
+                               h->cur_pic_ptr->field_poc[0] : 0,
+        .bottom_field_order_cnt = h->cur_pic_ptr->field_poc[1] != INT_MAX ?
+                                  h->cur_pic_ptr->field_poc[1] : 0,
+        .idr_pic_id = sl->idr_pic_id,
+        .pic_order_cnt_lsb = sl->poc_lsb,
+        .delta_pic_order_cnt_bottom = sl->delta_poc_bottom,
+        .delta_pic_order_cnt0 = sl->delta_poc[0],
+        .delta_pic_order_cnt1 = sl->delta_poc[1],
+        /* Size in bits of dec_ref_pic_marking() syntax element. */
+        .dec_ref_pic_marking_bit_size = sl->ref_pic_marking_bit_size,
+        /* Size in bits of pic order count syntax. */
+        .pic_order_cnt_bit_size = sl->pic_order_cnt_bit_size,
+        .slice_group_change_cycle = 0, /* slice group not supported by FFmpeg */
+    };
+
+    if (h->picture_idr)
+        controls->decode_params.flags |= V4L2_H264_DECODE_PARAM_FLAG_IDR_PIC;
+
+    if (FIELD_PICTURE(h))
+        controls->decode_params.flags |= V4L2_H264_DECODE_PARAM_FLAG_FIELD_PIC;
+
+    if (h->picture_structure == PICT_BOTTOM_FIELD)
+        controls->decode_params.flags |= V4L2_H264_DECODE_PARAM_FLAG_BOTTOM_FIELD;
+
+#if defined(V4L2_H264_DECODE_PARAM_FLAG_PFRAME)
+    if (sl->slice_type_nos == AV_PICTURE_TYPE_P)
+        controls->decode_params.flags |= V4L2_H264_DECODE_PARAM_FLAG_PFRAME;
+#endif
+
+#if defined(V4L2_H264_DECODE_PARAM_FLAG_BFRAME)
+    if (sl->slice_type_nos == AV_PICTURE_TYPE_B)
+        controls->decode_params.flags |= V4L2_H264_DECODE_PARAM_FLAG_BFRAME;
+#endif
+
+    fill_dpb(&controls->decode_params, h);
+
+    controls->first_slice = true;
+    controls->num_slices = 0;
+
+    return 0;
+}
+
+static int v4l2_request_h264_queue_decode(AVCodecContext *avctx, bool last_slice)
+{
+    const H264Context *h = avctx->priv_data;
+    V4L2RequestContextH264 *ctx = avctx->internal->hwaccel_priv_data;
+    V4L2RequestControlsH264 *controls = h->cur_pic_ptr->hwaccel_picture_private;
+
+    struct v4l2_ext_control control[] = {
+        {
+            .id = V4L2_CID_STATELESS_H264_SPS,
+            .ptr = &controls->sps,
+            .size = sizeof(controls->sps),
+        },
+        {
+            .id = V4L2_CID_STATELESS_H264_PPS,
+            .ptr = &controls->pps,
+            .size = sizeof(controls->pps),
+        },
+        {
+            .id = V4L2_CID_STATELESS_H264_SCALING_MATRIX,
+            .ptr = &controls->scaling_matrix,
+            .size = sizeof(controls->scaling_matrix),
+        },
+        {
+            .id = V4L2_CID_STATELESS_H264_DECODE_PARAMS,
+            .ptr = &controls->decode_params,
+            .size = sizeof(controls->decode_params),
+        },
+        {
+            .id = V4L2_CID_STATELESS_H264_SLICE_PARAMS,
+            .ptr = &controls->slice_params,
+            .size = sizeof(controls->slice_params),
+        },
+        {
+            .id = V4L2_CID_STATELESS_H264_PRED_WEIGHTS,
+            .ptr = &controls->pred_weights,
+            .size = sizeof(controls->pred_weights),
+        },
+    };
+
+    if (ctx->decode_mode == V4L2_STATELESS_H264_DECODE_MODE_SLICE_BASED) {
+        int count = FF_ARRAY_ELEMS(control) - (controls->pred_weights_required ? 0 : 1);
+        return ff_v4l2_request_decode_slice(avctx, &controls->pic, control, count,
+                                            controls->first_slice, last_slice);
+    }
+
+    return ff_v4l2_request_decode_frame(avctx, &controls->pic,
+                                        control, FF_ARRAY_ELEMS(control) - 2);
+}
+
+static int v4l2_request_h264_decode_slice(AVCodecContext *avctx,
+                                          const uint8_t *buffer, uint32_t size)
+{
+    const H264Context *h = avctx->priv_data;
+    const PPS *pps = h->ps.pps;
+    const H264SliceContext *sl = &h->slice_ctx[0];
+    V4L2RequestContextH264 *ctx = avctx->internal->hwaccel_priv_data;
+    V4L2RequestControlsH264 *controls = h->cur_pic_ptr->hwaccel_picture_private;
+    int i, ret, count;
+
+    if (ctx->decode_mode == V4L2_STATELESS_H264_DECODE_MODE_SLICE_BASED &&
+        controls->num_slices) {
+        ret = v4l2_request_h264_queue_decode(avctx, false);
+        if (ret)
+            return ret;
+
+        ff_v4l2_request_reset_picture(avctx, &controls->pic);
+        controls->first_slice = 0;
+    }
+
+    if (ctx->start_code == V4L2_STATELESS_H264_START_CODE_ANNEX_B) {
+        ret = ff_v4l2_request_append_output(avctx, &controls->pic,
+                                            nalu_slice_start_code, 3);
+        if (ret)
+            return ret;
+    }
+
+    ret = ff_v4l2_request_append_output(avctx, &controls->pic, buffer, size);
+    if (ret)
+        return ret;
+
+    if (ctx->decode_mode != V4L2_STATELESS_H264_DECODE_MODE_SLICE_BASED)
+        return 0;
+
+    controls->slice_params = (struct v4l2_ctrl_h264_slice_params) {
+        /* Offset in bits to slice_data() from the beginning of this slice. */
+        .header_bit_size = get_bits_count(&sl->gb),
+
+        .first_mb_in_slice = sl->first_mb_addr,
+
+        .slice_type = ff_h264_get_slice_type(sl),
+        .colour_plane_id = 0, /* separate colour plane not supported by FFmpeg */
+        .redundant_pic_cnt = sl->redundant_pic_count,
+        .cabac_init_idc = sl->cabac_init_idc,
+        .slice_qp_delta = sl->qscale - pps->init_qp,
+        .slice_qs_delta = 0, /* not implemented by FFmpeg */
+        .disable_deblocking_filter_idc = sl->deblocking_filter < 2 ?
+                                         !sl->deblocking_filter :
+                                         sl->deblocking_filter,
+        .slice_alpha_c0_offset_div2 = sl->slice_alpha_c0_offset / 2,
+        .slice_beta_offset_div2 = sl->slice_beta_offset / 2,
+        .num_ref_idx_l0_active_minus1 = sl->list_count > 0 ? sl->ref_count[0] - 1 : 0,
+        .num_ref_idx_l1_active_minus1 = sl->list_count > 1 ? sl->ref_count[1] - 1 : 0,
+    };
+
+    if (sl->slice_type == AV_PICTURE_TYPE_B && sl->direct_spatial_mv_pred)
+        controls->slice_params.flags |= V4L2_H264_SLICE_FLAG_DIRECT_SPATIAL_MV_PRED;
+
+    /* V4L2_H264_SLICE_FLAG_SP_FOR_SWITCH: not implemented by FFmpeg */
+
+    controls->pred_weights_required =
+        V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED(&controls->pps, &controls->slice_params);
+    if (controls->pred_weights_required) {
+        controls->pred_weights.chroma_log2_weight_denom = sl->pwt.chroma_log2_weight_denom;
+        controls->pred_weights.luma_log2_weight_denom = sl->pwt.luma_log2_weight_denom;
+    }
+
+    count = sl->list_count > 0 ? sl->ref_count[0] : 0;
+    for (i = 0; i < count; i++)
+        fill_ref_list(&controls->slice_params.ref_pic_list0[i],
+                      &controls->decode_params, &sl->ref_list[0][i]);
+    if (count && controls->pred_weights_required)
+        fill_weight_factors(&controls->pred_weights.weight_factors[0], 0, sl);
+
+    count = sl->list_count > 1 ? sl->ref_count[1] : 0;
+    for (i = 0; i < count; i++)
+        fill_ref_list(&controls->slice_params.ref_pic_list1[i],
+                      &controls->decode_params, &sl->ref_list[1][i]);
+    if (count && controls->pred_weights_required)
+        fill_weight_factors(&controls->pred_weights.weight_factors[1], 1, sl);
+
+    controls->num_slices++;
+    return 0;
+}
+
+static int v4l2_request_h264_end_frame(AVCodecContext *avctx)
+{
+    return v4l2_request_h264_queue_decode(avctx, true);
+}
+
+static int v4l2_request_h264_post_probe(AVCodecContext *avctx)
+{
+    V4L2RequestContextH264 *ctx = avctx->internal->hwaccel_priv_data;
+
+    struct v4l2_ext_control control[] = {
+        { .id = V4L2_CID_STATELESS_H264_DECODE_MODE, },
+        { .id = V4L2_CID_STATELESS_H264_START_CODE, },
+    };
+
+    ctx->decode_mode = ff_v4l2_request_query_control_default_value(avctx,
+                                            V4L2_CID_STATELESS_H264_DECODE_MODE);
+    if (ctx->decode_mode != V4L2_STATELESS_H264_DECODE_MODE_SLICE_BASED &&
+        ctx->decode_mode != V4L2_STATELESS_H264_DECODE_MODE_FRAME_BASED) {
+        av_log(ctx, AV_LOG_VERBOSE, "Unsupported decode mode: %d\n",
+               ctx->decode_mode);
+        return AVERROR(EINVAL);
+    }
+
+    ctx->start_code = ff_v4l2_request_query_control_default_value(avctx,
+                                            V4L2_CID_STATELESS_H264_START_CODE);
+    if (ctx->start_code != V4L2_STATELESS_H264_START_CODE_NONE &&
+        ctx->start_code != V4L2_STATELESS_H264_START_CODE_ANNEX_B) {
+        av_log(ctx, AV_LOG_VERBOSE, "Unsupported start code: %d\n",
+               ctx->start_code);
+        return AVERROR(EINVAL);
+    }
+
+    // TODO: check V4L2_CID_MPEG_VIDEO_H264_PROFILE control
+    // TODO: check V4L2_CID_MPEG_VIDEO_H264_LEVEL control
+
+    control[0].value = ctx->decode_mode;
+    control[1].value = ctx->start_code;
+
+    return ff_v4l2_request_set_controls(avctx, control, FF_ARRAY_ELEMS(control));
+}
+
+static int v4l2_request_h264_init(AVCodecContext *avctx)
+{
+    V4L2RequestContextH264 *ctx = avctx->internal->hwaccel_priv_data;
+    const H264Context *h = avctx->priv_data;
+    struct v4l2_ctrl_h264_sps sps;
+    int ret;
+
+    struct v4l2_ext_control control[] = {
+        {
+            .id = V4L2_CID_STATELESS_H264_SPS,
+            .ptr = &sps,
+            .size = sizeof(sps),
+        },
+    };
+
+    fill_sps(&sps, h);
+
+    ctx->base.post_probe = v4l2_request_h264_post_probe;
+    return ff_v4l2_request_init(avctx, V4L2_PIX_FMT_H264_SLICE,
+                                4 * 1024 * 1024,
+                                control, FF_ARRAY_ELEMS(control));
+}
+
+const FFHWAccel ff_h264_v4l2request_hwaccel = {
+    .p.name             = "h264_v4l2request",
+    .p.type             = AVMEDIA_TYPE_VIDEO,
+    .p.id               = AV_CODEC_ID_H264,
+    .p.pix_fmt          = AV_PIX_FMT_DRM_PRIME,
+    .start_frame        = v4l2_request_h264_start_frame,
+    .decode_slice       = v4l2_request_h264_decode_slice,
+    .end_frame          = v4l2_request_h264_end_frame,
+    .flush              = ff_v4l2_request_flush,
+    .frame_priv_data_size = sizeof(V4L2RequestControlsH264),
+    .init               = v4l2_request_h264_init,
+    .uninit             = ff_v4l2_request_uninit,
+    .priv_data_size     = sizeof(V4L2RequestContextH264),
+    .frame_params       = ff_v4l2_request_frame_params,
+};