[FFmpeg-devel] [PATCH] nvdec/vc1: add marker insertion logic

[averne <averne381@gmail.com>]

---
Insert the relevant marker into the bitstream on
slice submission.
This is analogous to the logic found in DXVA and
D3D hwaccels.

Fixes decoding of various VC-1 streams, eg.:
https://drive.google.com/file/d/1WJyiRhcdU4FHTW3sVMitS7UdrZM1NBy-/view?usp=sharing

This was investigated using my nvdec tracing tool:
https://github.com/averne/NvdecTrace

Signed-off-by: averne <averne381@gmail.com>
---
 libavcodec/nvdec_vc1.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/libavcodec/nvdec_vc1.c b/libavcodec/nvdec_vc1.c
index fbfba1ecb43421573ef8fea1e37a2425c272edc9..2726574a26583b0cfc28bdec5595c15bdc465ff8 100644
--- a/libavcodec/nvdec_vc1.c
+++ b/libavcodec/nvdec_vc1.c
@@ -22,6 +22,7 @@
 
 #include "config_components.h"
 
+#include "libavutil/mem.h"
 #include "avcodec.h"
 #include "hwaccel_internal.h"
 #include "internal.h"
@@ -107,6 +108,51 @@ static int nvdec_vc1_start_frame(AVCodecContext *avctx, const uint8_t *buffer, u
     return 0;
 }
 
+static int nvdec_vc1_decode_slice(AVCodecContext *avctx, const uint8_t *buffer,
+                                  uint32_t size)
+{
+    NVDECContext *ctx = avctx->internal->hwaccel_priv_data;
+    const VC1Context *v = avctx->priv_data;
+    uint32_t marker;
+    int marker_size;
+    void *tmp;
+
+    if (avctx->codec_id != AV_CODEC_ID_VC1) {
+        marker_size = 0;
+    } else {
+        if (ctx->bitstream_len)
+            marker = VC1_CODE_SLICE;
+        else if (v->profile == PROFILE_ADVANCED && v->fcm == ILACE_FIELD && v->second_field)
+            marker = VC1_CODE_FIELD;
+        else
+            marker = VC1_CODE_FRAME;
+
+        marker_size = (size >= sizeof(marker) && AV_RB32(buffer) != marker) ? sizeof(marker) : 0;
+    }
+
+    tmp = av_fast_realloc(ctx->bitstream_internal, &ctx->bitstream_allocated,
+                          ctx->bitstream_len + size + marker_size);
+    if (!tmp)
+        return AVERROR(ENOMEM);
+    ctx->bitstream = ctx->bitstream_internal = tmp;
+
+    tmp = av_fast_realloc(ctx->slice_offsets, &ctx->slice_offsets_allocated,
+                          (ctx->nb_slices + 1) * sizeof(*ctx->slice_offsets));
+    if (!tmp)
+        return AVERROR(ENOMEM);
+    ctx->slice_offsets = tmp;
+
+    if (marker_size)
+        AV_WB32(ctx->bitstream_internal + ctx->bitstream_len, marker);
+
+    memcpy(ctx->bitstream_internal + ctx->bitstream_len + marker_size, buffer, size);
+    ctx->slice_offsets[ctx->nb_slices] = ctx->bitstream_len;
+    ctx->bitstream_len += size + marker_size;
+    ctx->nb_slices++;
+
+    return 0;
+}
+
 static int nvdec_vc1_frame_params(AVCodecContext *avctx,
                                   AVBufferRef *hw_frames_ctx)
 {
@@ -121,7 +167,7 @@ const FFHWAccel ff_vc1_nvdec_hwaccel = {
     .p.pix_fmt            = AV_PIX_FMT_CUDA,
     .start_frame          = nvdec_vc1_start_frame,
     .end_frame            = ff_nvdec_simple_end_frame,
-    .decode_slice         = ff_nvdec_simple_decode_slice,
+    .decode_slice         = nvdec_vc1_decode_slice,
     .frame_params         = nvdec_vc1_frame_params,
     .init                 = ff_nvdec_decode_init,
     .uninit               = ff_nvdec_decode_uninit,
@@ -136,7 +182,7 @@ const FFHWAccel ff_wmv3_nvdec_hwaccel = {
     .p.pix_fmt            = AV_PIX_FMT_CUDA,
     .start_frame          = nvdec_vc1_start_frame,
     .end_frame            = ff_nvdec_simple_end_frame,
-    .decode_slice         = ff_nvdec_simple_decode_slice,
+    .decode_slice         = nvdec_vc1_decode_slice,
     .frame_params         = nvdec_vc1_frame_params,
     .init                 = ff_nvdec_decode_init,
     .uninit               = ff_nvdec_decode_uninit,

---
base-commit: f76195ff656d6bea68feee783160652e2b3e3d60
change-id: 20250304-nvdec-vc1-marker2-53d6bd30ee99

Best regards,
-- 
averne <averne381@gmail.com>

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