[FFmpeg-devel] [PATCH v2] nvdec/vc1: add marker insertion logic

[averne <averne381@gmail.com>]

This mirrors existing code in d3dxx and dxva hwaccels

---
Changes since v1: use the codec-specific handler 
for wmv3.

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 | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/libavcodec/nvdec_vc1.c b/libavcodec/nvdec_vc1.c
index fbfba1ecb43421573ef8fea1e37a2425c272edc9..a88327833df55054a42e7ced8cdd4c99fa6b6584 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 +108,48 @@ 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 (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;
+
+    /* Only insert the marker if not already present in the bitstream */
+    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 +164,7 @@ 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,

---
base-commit: f76195ff656d6bea68feee783160652e2b3e3d60
change-id: 20250408-nvdec-vc1-fix-7fb117513851

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

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