diff --git a/src/core/ggml_extend.hpp b/src/core/ggml_extend.hpp
index ba087d3c..ebbed10b 100644
--- a/src/core/ggml_extend.hpp
+++ b/src/core/ggml_extend.hpp
@@ -1038,6 +1038,7 @@ __STATIC_INLINE__ ggml_tensor* ggml_ext_linear(ggml_context* ctx,
 }
 
 __STATIC_INLINE__ ggml_tensor* ggml_ext_pad_ext(ggml_context* ctx,
+                                                ggml_backend_t backend,
                                                 ggml_tensor* x,
                                                 int lp0,
                                                 int rp0,
@@ -1063,7 +1064,17 @@ __STATIC_INLINE__ ggml_tensor* ggml_ext_pad_ext(ggml_context* ctx,
     }
 
     if (lp0 != 0 || rp0 != 0 || lp1 != 0 || rp1 != 0 || lp2 != 0 || rp2 != 0 || lp3 != 0 || rp3 != 0) {
-        x = ggml_pad_ext(ctx, x, lp0, rp0, lp1, rp1, lp2, rp2, lp3, rp3);
+        ggml_tensor* padded = ggml_pad_ext(ctx, x, lp0, rp0, lp1, rp1, lp2, rp2, lp3, rp3);
+        if (backend == nullptr || ggml_backend_supports_op(backend, padded)) {
+            x = padded;
+        } else {
+            // Some backends (e.g. Metal) only implement right-padding for
+            // GGML_OP_PAD (see #850): pad right by lp+rp instead, then roll
+            // the padding around to the left. shift < ne always holds because
+            // ne grew by lp+rp.
+            x = ggml_pad_ext(ctx, x, 0, lp0 + rp0, 0, lp1 + rp1, 0, lp2 + rp2, 0, lp3 + rp3);
+            x = ggml_roll(ctx, x, lp0, lp1, lp2, lp3);
+        }
     }
     return x;
 }
@@ -1076,7 +1087,7 @@ __STATIC_INLINE__ ggml_tensor* ggml_ext_pad(ggml_context* ctx,
                                             int p3          = 0,
                                             bool circular_x = false,
                                             bool circular_y = false) {
-    return ggml_ext_pad_ext(ctx, x, 0, p0, 0, p1, 0, p2, 0, p3, circular_x, circular_y);
+    return ggml_ext_pad_ext(ctx, nullptr, x, 0, p0, 0, p1, 0, p2, 0, p3, circular_x, circular_y);
 }
 
 // w: [OC，IC, KH, KW]
@@ -1105,7 +1116,7 @@ __STATIC_INLINE__ ggml_tensor* ggml_ext_conv_2d(ggml_context* ctx,
     }
 
     if ((p0 != 0 || p1 != 0) && (circular_x || circular_y)) {
-        x  = ggml_ext_pad_ext(ctx, x, p0, p0, p1, p1, 0, 0, 0, 0, circular_x, circular_y);
+        x  = ggml_ext_pad_ext(ctx, nullptr, x, p0, p0, p1, p1, 0, 0, 0, 0, circular_x, circular_y);
         p0 = 0;
         p1 = 0;
     }
@@ -1130,6 +1141,7 @@ __STATIC_INLINE__ ggml_tensor* ggml_ext_conv_2d(ggml_context* ctx,
 // b: [OC,]
 // result: [N*OC, OD, OH, OW]
 __STATIC_INLINE__ ggml_tensor* ggml_ext_conv_3d(ggml_context* ctx,
+                                                ggml_backend_t backend,
                                                 ggml_tensor* x,
                                                 ggml_tensor* w,
                                                 ggml_tensor* b,
@@ -1159,7 +1171,21 @@ __STATIC_INLINE__ ggml_tensor* ggml_ext_conv_3d(ggml_context* ctx,
         x          = ggml_cont(ctx, ggml_permute(ctx, x, 0, 1, 3, 2));
         x          = ggml_reshape_4d(ctx, x, im2col->ne[1], im2col->ne[2], OD, OC * N);
     } else {
-        x = ggml_conv_3d(ctx, w, x, IC, s0, s1, s2, p0, p1, p2, d0, d1, d2);
+        // ggml_conv_3d decomposes into GGML_OP_IM2COL_3D, which some backends
+        // (e.g. Metal, see #850) do not implement. Fall back to
+        // GGML_OP_CONV_3D on those backends.
+        bool im2col_3d_supported = true;
+        if (backend != nullptr) {
+            ggml_tensor* im2col = ggml_im2col_3d(ctx, w, x, IC, s0, s1, s2, p0, p1, p2, d0, d1, d2, w->type);
+            im2col_3d_supported = ggml_backend_supports_op(backend, im2col);
+        }
+        if (im2col_3d_supported) {
+            x = ggml_conv_3d(ctx, w, x, IC, s0, s1, s2, p0, p1, p2, d0, d1, d2);
+        } else {
+            int64_t OC = w->ne[3] / IC;
+            int64_t N  = x->ne[3] / IC;
+            x          = ggml_conv_3d_direct(ctx, w, x, s0, s1, s2, p0, p1, p2, d0, d1, d2, (int)IC, (int)N, (int)OC);
+        }
     }
 
     if (b != nullptr) {
@@ -3368,7 +3394,7 @@ public:
                 b = ctx->weight_adapter->patch_weight(ctx->ggml_ctx, ctx->backend, b, prefix + "bias");
             }
         }
-        return ggml_ext_conv_3d(ctx->ggml_ctx, x, w, b, in_channels,
+        return ggml_ext_conv_3d(ctx->ggml_ctx, ctx->backend, x, w, b, in_channels,
                                 std::get<2>(stride), std::get<1>(stride), std::get<0>(stride),
                                 std::get<2>(padding), std::get<1>(padding), std::get<0>(padding),
                                 std::get<2>(dilation), std::get<1>(dilation), std::get<0>(dilation),
diff --git a/src/model/vae/ltx_audio_vae.hpp b/src/model/vae/ltx_audio_vae.hpp
index 2f8c03d1..71070d6a 100644
--- a/src/model/vae/ltx_audio_vae.hpp
+++ b/src/model/vae/ltx_audio_vae.hpp
@@ -214,7 +214,7 @@ namespace LTXV {
 
         auto x = ggml_reshape_3d(ctx, waveform, time, 1, channels * batch);
         if (left_pad > 0) {
-            x = ggml_pad_ext(ctx, x, static_cast<int>(left_pad), 0, 0, 0, 0, 0, 0, 0);
+            x = ggml_ext_pad_ext(ctx, runner_ctx->backend, x, static_cast<int>(left_pad), 0, 0, 0, 0, 0, 0, 0);
         }
 
         auto frames = ggml_conv_1d(ctx, forward_basis, x, hop_length, 0, 1);
@@ -451,6 +451,7 @@ namespace LTXV {
             int pad_h = kernel_size.first - 1;
             int pad_w = kernel_size.second - 1;
             x         = ggml_ext_pad_ext(ctx->ggml_ctx,
+                                         ctx->backend,
                                          x,
                                          pad_w / 2,
                                          pad_w - pad_w / 2,
diff --git a/src/model/vae/tae.hpp b/src/model/vae/tae.hpp
index a78e5e96..558c0544 100644
--- a/src/model/vae/tae.hpp
+++ b/src/model/vae/tae.hpp
@@ -408,7 +408,7 @@ public:
             h = conv->forward(ctx, h);
             for (int j = 0; j < num_blocks; j++) {
                 auto block = std::dynamic_pointer_cast<MemBlock>(blocks[std::to_string(index++)]);
-                auto mem   = ggml_pad_ext(ctx->ggml_ctx, h, 0, 0, 0, 0, 0, 0, 1, 0);
+                auto mem   = ggml_ext_pad_ext(ctx->ggml_ctx, ctx->backend, h, 0, 0, 0, 0, 0, 0, 1, 0);
                 mem        = ggml_view_4d(ctx->ggml_ctx, mem, h->ne[0], h->ne[1], h->ne[2], h->ne[3], h->nb[1], h->nb[2], h->nb[3], 0);
                 h          = block->forward(ctx, h, mem);
             }
@@ -479,7 +479,7 @@ public:
         int index = 3;
         for (int i = 0; i < num_layers; i++) {
             for (int j = 0; j < num_blocks; j++) {
-                auto mem = ggml_pad_ext(ctx->ggml_ctx, h, 0, 0, 0, 0, 0, 0, 1, 0);
+                auto mem = ggml_ext_pad_ext(ctx->ggml_ctx, ctx->backend, h, 0, 0, 0, 0, 0, 0, 1, 0);
                 mem      = ggml_view_4d(ctx->ggml_ctx, mem, h->ne[0], h->ne[1], h->ne[2], h->ne[3], h->nb[1], h->nb[2], h->nb[3], 0);
                 if (is_wide) {
                     auto block = std::dynamic_pointer_cast<WideMemBlock>(blocks[std::to_string(index++)]);
diff --git a/src/model/vae/wan_vae.hpp b/src/model/vae/wan_vae.hpp
index d28b5b25..94956209 100644
--- a/src/model/vae/wan_vae.hpp
+++ b/src/model/vae/wan_vae.hpp
@@ -72,8 +72,8 @@ namespace WAN {
                 lp2 -= (int)cache_x->ne[2];
             }
 
-            x = ggml_ext_pad_ext(ctx->ggml_ctx, x, lp0, rp0, lp1, rp1, lp2, rp2, 0, 0, ctx->circular_x_enabled, ctx->circular_y_enabled);
-            return ggml_ext_conv_3d(ctx->ggml_ctx, x, w, b, in_channels,
+            x = ggml_ext_pad_ext(ctx->ggml_ctx, ctx->backend, x, lp0, rp0, lp1, rp1, lp2, rp2, 0, 0, ctx->circular_x_enabled, ctx->circular_y_enabled);
+            return ggml_ext_conv_3d(ctx->ggml_ctx, ctx->backend, x, w, b, in_channels,
                                     std::get<2>(stride), std::get<1>(stride), std::get<0>(stride),
                                     0, 0, 0,
                                     std::get<2>(dilation), std::get<1>(dilation), std::get<0>(dilation));
@@ -195,7 +195,7 @@ namespace WAN {
                                                   2);
                         }
                         if (chunk_idx == 1 && cache_x->ne[2] < 2) {  // Rep
-                            cache_x = ggml_pad_ext(ctx->ggml_ctx, cache_x, 0, 0, 0, 0, (int)cache_x->ne[2], 0, 0, 0);
+                            cache_x = ggml_ext_pad_ext(ctx->ggml_ctx, ctx->backend, cache_x, 0, 0, 0, 0, (int)cache_x->ne[2], 0, 0, 0);
                             // aka cache_x = torch.cat([torch.zeros_like(cache_x).to(cache_x.device),cache_x],dim=2)
                         }
                         if (chunk_idx == 1) {
@@ -283,7 +283,7 @@ namespace WAN {
 
             int pad_t = (factor_t - T % factor_t) % factor_t;
 
-            x = ggml_pad_ext(ctx->ggml_ctx, x, 0, 0, 0, 0, pad_t, 0, 0, 0);
+            x = ggml_ext_pad_ext(ctx->ggml_ctx, ctx->backend, x, 0, 0, 0, 0, pad_t, 0, 0, 0);
             T = x->ne[2];
 
             x = ggml_reshape_4d(ctx->ggml_ctx, x, W * H, factor_t, T / factor_t, C);                                                  // [C, T/factor_t, factor_t, H*W]