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fix: match reference first-chunk semantics in Wan VAE temporal upsample #21

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olyasir merged 2 commits into from
Jul 17, 2026
Merged

fix: match reference first-chunk semantics in Wan VAE temporal upsample #21

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cc76eb1
fix: match reference first-chunk semantics in Wan VAE temporal upsample
olyasir Jul 17, 2026
e17495a
fix: assert time_conv block exists before use in upsample3d path
olyasir Jul 17, 2026
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42 changes: 23 additions & 19 deletions src/wan.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -166,32 +166,36 @@ namespace WAN {
if (feat_cache.size() > 0) {
int idx = feat_idx;
feat_idx += 1;
if (chunk_idx == 0) {
// feat_cache[idx] == nullptr, pass
auto time_conv_it = blocks.find("time_conv");
GGML_ASSERT(time_conv_it != blocks.end());
auto time_conv = std::dynamic_pointer_cast<CausalConv3d>(time_conv_it->second);
GGML_ASSERT(time_conv != nullptr);

// mirrors the reference (vae2_2.py Resample.forward):
// cache_x = x[:, :, -CACHE_T:].clone()
// if feat_cache[idx] == "Rep": x = time_conv(x) # chunk 0: causal zero pad
// else: <prepend last cached frame if short>; x = time_conv(x, feat_cache[idx])
// feat_cache[idx] = cache_x
auto cache_x = ggml_ext_slice(ctx->ggml_ctx, x, 2, -CACHE_T, x->ne[2]);
if (chunk_idx == 0) { // "Rep"
x = time_conv->forward(ctx, x);
} else {
auto time_conv = std::dynamic_pointer_cast<CausalConv3d>(blocks["time_conv"]);

auto cache_x = ggml_ext_slice(ctx->ggml_ctx, x, 2, -CACHE_T, x->ne[2]);
if (cache_x->ne[2] < 2 && feat_cache[idx] != nullptr) { // chunk_idx >= 2
if (cache_x->ne[2] < 2 && feat_cache[idx] != nullptr) {
// cache last frame of last two chunk
cache_x = ggml_concat(ctx->ggml_ctx,
ggml_ext_slice(ctx->ggml_ctx, feat_cache[idx], 2, -1, feat_cache[idx]->ne[2]),
cache_x,
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);
// aka cache_x = torch.cat([torch.zeros_like(cache_x).to(cache_x.device),cache_x],dim=2)
}
if (chunk_idx == 1) {
x = time_conv->forward(ctx, x);
} else {
x = time_conv->forward(ctx, x, feat_cache[idx]);
}
feat_cache[idx] = cache_x;
x = ggml_reshape_4d(ctx->ggml_ctx, x, w * h, t, c, 2); // (2, c, t, h*w)
x = ggml_ext_cont(ctx->ggml_ctx, ggml_ext_torch_permute(ctx->ggml_ctx, x, 0, 3, 1, 2)); // (c, t, 2, h*w)
x = ggml_reshape_4d(ctx->ggml_ctx, x, w, h, 2 * t, c); // (c, t*2, h, w)
x = time_conv->forward(ctx, x, feat_cache[idx]);
}
feat_cache[idx] = cache_x;
x = ggml_reshape_4d(ctx->ggml_ctx, x, w * h, t, c, 2); // (2, c, t, h*w)
x = ggml_ext_cont(ctx->ggml_ctx, ggml_ext_torch_permute(ctx->ggml_ctx, x, 0, 3, 1, 2)); // (c, t, 2, h*w)
x = ggml_reshape_4d(ctx->ggml_ctx, x, w, h, 2 * t, c); // (c, t*2, h, w)
if (chunk_idx == 0) {
// reference: if first_chunk: x = x[:, :, 1:]
x = ggml_ext_slice(ctx->ggml_ctx, x, 2, 1, x->ne[2]);
}
}
}
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