I am working on a video animation project using PyTorch. My dataset contains 3904x60 mfcc audio features(input) and corresponding 3904x3 video features(output). The goal is to train a neural network model such that given an unknown audio feature, the model maps it into its corresponding video feature. In other words, the neural network performs a 60 to 3 feature mapping. I have already built the neural network following this tutorial and my CNN architecture looks like:

```
class ConvNet(nn.Module):
def __init__(self):
super().__init__()
self.layer1 = nn.Sequential(
nn.Conv1d(1, 32, kernel_size=5, stride=1, padding=2),
nn.ReLU(),
nn.MaxPool1d(kernel_size=2, stride=2))
self.layer2 = nn.Sequential(
nn.Conv1d(32, 64, kernel_size=5, stride=1, padding=2),
nn.ReLU(),
nn.MaxPool1d(kernel_size=2, stride=2))
self.drop_out = nn.Dropout()
self.fc1 = nn.Linear(15 * 64, 1000)
self.fc2 = nn.Linear(1000, 3)
def forward(self, x):
out = self.layer1(x)
out = self.layer2(out)
out = out.reshape(out.size(0), -1)
out = self.drop_out(out)
out = self.fc1(out)
out = self.fc2(out)
return out
```

and my training code looks like:

```
model = ConvNet()
criterion = nn.CrossEntropyLoss()
optimizer = torch.optim.Adam(model.parameters(), lr=learning_rate)
for epoch in range(num_epochs):
for i, (a, v) in enumerate(train_loader):
# Run the forward pass
a = a.float()
v = v.long()
outputs = model(a.view(a.size(0),1,a.size(1)))
loss = criterion(outputs, v)
loss_list.append(loss.item())
# Backprop and perform Adam optimisation
optimizer.zero_grad()
loss.backward()
optimizer.step()
# Track the accuracy
total = labels.size(0)
_, predicted = torch.max(outputs.data, 1)
correct = (predicted == labels).sum().item()
acc_list.append(correct / total)
if (i + 1) % 100 == 0:
print('Epoch[{}/{}],Step[{}/{}],Loss{:.4f},Accuracy{:.2f}%'
.format(epoch + 1, num_epochs, i + 1, total_step, loss.item(),
(correct / total) * 100))
```

But as I ran the code I received an error:

—> 13 loss = criterion(outputs, v)

RuntimeError: multi-target not supported at /Users/soumith/miniconda2/conda-bld/pytorch_1532623076075/work/aten/src/THNN/generic/ClassNLLCriterion.c:21

I defined the batch size to be 4 so each a and v in the iteration should be a 4 by 60 tensor and a 4 by 3 tensor, respectively. One solution suggests that I should reshape the tensor into a categorical vector. However, this solution doesn’t actually apply to this case since I want the 3 output feature integrated as a whole instead of treating each feature as an independent label. How do I solve this problem?