ctc_loss error "No valid path found."

It turns out that the ctc_loss requires that the label lengths be shorter than the input lengths. If the label lengths are too long, the loss calculator cannot unroll completely and therefore cannot compute the loss.

For example, the label BIFI would require input length of at least 4 while the label BIIF would require input length of at least 5 due to a blank being inserted between the repeated symbols.

I had the same issue but I soon realized it was just because I was using glob and my label was in the filename so it was exceeding.

You can fix this issue by using:

os.path.join(*(filename.split(os.path.sep)[noOfDir:]))