h5toh4 performs a basic conversion designed to meet common requirements; it does 
not attempt to convert every HDF5 object that a file might contain.

The following describes some of the tool’s limitations:

1. Limited datatypes conversions
h5toh4 does not convert datasets of the following datatypes:
  Array
  Multi-dimensional strings
  Bitfield
  Time
The tool issues a warning message and skips the dataset, but continues to process 
 the file.

2. Unrecognized datatypes
h5toh4 issues an error and exits upon encountering a dataset of the following 
datatypes:

  Object reference
  Region reference
  ENUM
  Any variable-length datatype

3. Compound datatype
When h5toh4 encounters a dataset of the following datatype, it causes a 
segmentation fault:

Compound datatype with a field of array datatype and 5 or more dimensions
The tool successfully processes compound datatypes with fields of array 
datatype and 4 or fewer dimensions.

4. Dimension scales
h5toh4 does not support dimension scale datasets; they are treated as regular 
datasets in HDF5 and SDSs in the conversion to HDF4.

5. Unlimited dimensions
HDF4 allows only one unlimited dimension, so h5toh4 is limited in its ability 
to convert HDF5 datasets with unlimited dimensions.
If the first dimension of an HDF5 dataset is unlimited, that is:
If dim[0]=H5S_UNLIMITED, then h5toh4 will set that dimension to unlimited in 
the resulting HDF4 dataset. Other dimensions will be set in the HDF4 file to 
their current size in the HDF5 file.

6. Number of objects
An HDF4 file is limited to 20,000 objects. h5toh4 cannot support file conversions 
that would exceed that limit (and its behavior in such situations is not tested).

7. File size
h5toh4 can convert files up to 2 GB in size; it will exit with code 1 if the 
source HDF5 file is larger than 2 GB.
