diff --git a/caiman/tests/test_sbx.py b/caiman/tests/test_sbx.py
index d8609edaa..cba2abf63 100644
--- a/caiman/tests/test_sbx.py
+++ b/caiman/tests/test_sbx.py
@@ -29,6 +29,7 @@ def test_load_2d():
     assert data_2d.ndim == 3, 'Loaded 2D data has wrong dimensionality'
     assert data_2d.shape == SHAPE_2D, 'Loaded 2D data has wrong shape'
     assert data_2d.shape == (meta_2d['num_frames'], *meta_2d['frame_size']), 'Shape in metadata does not match loaded data'
+    assert meta_2d['frame_rate'] == 15.625, 'Frame rate in metadata is incorrect (unidirectional)'
     npt.assert_array_equal(data_2d[0, 0, :10], [712, 931, 1048, 825, 1383, 882, 601, 798, 1022, 966], 'Loaded 2D data has wrong values')
 
     data_2d_movie = cm.load(file_2d)
@@ -37,6 +38,23 @@ def test_load_2d():
     npt.assert_array_almost_equal(data_2d_movie, data_2d, err_msg='Movie loaded with cm.load has wrong values')
 
 
+def test_load_2d_bidi():
+    file_2d_bidi = os.path.join(TESTDATA_PATH, '2d_sbx_bidi.sbx')
+    data_2d_bidi = sbx_utils.sbxread(file_2d_bidi)
+    meta_2d_bidi = sbx_utils.sbx_meta_data(file_2d_bidi)
+
+    assert data_2d_bidi.ndim == 3, 'Loaded 2D bidirectional data has wrong dimensionality'
+    assert data_2d_bidi.shape == SHAPE_2D, 'Loaded 2D bidirectional data has wrong shape'
+    assert data_2d_bidi.shape == (meta_2d_bidi['num_frames'], *meta_2d_bidi['frame_size']), 'Shape in metadata does not match loaded data'
+    assert meta_2d_bidi['frame_rate'] == 31.25, 'Frame rate in metadata is incorrect (bidirectional)'
+    npt.assert_array_equal(data_2d_bidi[0, 0, :10], [2833, 1538, 1741, 1837, 2079, 2038, 1946, 1631, 2260, 2073], 'Loaded 2D bidirectional data has wrong values')
+
+    data_2d_bidi_movie = cm.load(file_2d_bidi)
+    assert data_2d_bidi_movie.ndim == data_2d_bidi.ndim, 'Movie loaded with cm.load has wrong dimensionality'
+    assert data_2d_bidi_movie.shape == data_2d_bidi.shape, 'Movie loaded with cm.load has wrong shape'
+    npt.assert_array_almost_equal(data_2d_bidi_movie, data_2d_bidi, err_msg='Movie loaded with cm.load has wrong values')
+
+
 def test_load_3d():
     file_3d = os.path.join(TESTDATA_PATH, '3d_sbx_1.sbx')
     data_3d = sbx_utils.sbxread(file_3d)
@@ -45,6 +63,7 @@ def test_load_3d():
     assert data_3d.ndim == 4, 'Loaded 3D data has wrong dimensionality'
     assert data_3d.shape == SHAPE_3D, 'Loaded 3D data has wrong shape'
     assert data_3d.shape == (meta_3d['num_frames'], *meta_3d['frame_size'], meta_3d['num_planes']), 'Shape in metadata does not match loaded data'
+    assert meta_3d['frame_rate'] == 15.625 / meta_3d['num_planes'], 'Frame rate in metadata is incorrect (bidirectional 3D)'
     npt.assert_array_equal(data_3d[0, 0, :10, 0], [2167, 2525, 1713, 1747, 1887, 1741, 1873, 1244, 1747, 1637], 'Loaded 2D data has wrong values')
 
     data_3d_movie = cm.load(file_3d, is3D=True)
diff --git a/caiman/utils/sbx_utils.py b/caiman/utils/sbx_utils.py
index 48bbba484..610b1be93 100644
--- a/caiman/utils/sbx_utils.py
+++ b/caiman/utils/sbx_utils.py
@@ -9,13 +9,13 @@
 import os
 import scipy
 import tifffile
-from typing import Iterable, Union, Optional
+from typing import Any, Sequence, Union, Optional, cast
 
-DimSubindices = Union[Iterable[int], slice]
-FileSubindices = Union[DimSubindices, Iterable[DimSubindices]]  # can have inds for just frames or also for y, x, z
-ChainSubindices = Union[FileSubindices, Iterable[FileSubindices]]  # one to apply to each file, or separate for each file
+DimSubindices = Union[Sequence[int], slice]
+FileSubindices = Union[DimSubindices, Sequence[DimSubindices]]  # can have inds for just frames or also for y, x, z
+ChainSubindices = Union[FileSubindices, Sequence[FileSubindices]]  # one to apply to each file, or separate for each file
 
-def loadmat_sbx(filename: str) -> dict:
+def loadmat_sbx(filename: str) -> dict[str, Any]:
     """
     this wrapper should be called instead of directly calling spio.loadmat
 
@@ -25,7 +25,7 @@ def loadmat_sbx(filename: str) -> dict:
     """
     data_ = scipy.io.loadmat(filename, struct_as_record=False, squeeze_me=True)
     _check_keys(data_)
-    return data_
+    return data_['info']
 
 
 def _check_keys(checkdict: dict) -> None:
@@ -135,7 +135,7 @@ def sbx_chain_to_tif(filenames: list[str], fileout: str, subindices: Optional[Ch
         fileout: str
             filename to save, including the .tif suffix
         
-        subindices:  Iterable[int] | slice | Iterable[Iterable[int] | slice | tuple[Iterable[int] | slice, ...]]
+        subindices:  Sequence[int] | slice | Sequence[Sequence[int] | slice | tuple[Sequence[int] | slice, ...]]
             see subindices for sbx_to_tif
             can specify separate subindices for each file if nested 2 levels deep; 
             X, Y, and Z sizes must match for all files after indexing.
@@ -146,21 +146,25 @@ def sbx_chain_to_tif(filenames: list[str], fileout: str, subindices: Optional[Ch
         subindices = slice(None)
 
     # Validate aggressively to avoid failing after waiting to copy a lot of data
-    if isinstance(subindices, slice) or np.isscalar(subindices[0]):
-        # One set of subindices to repeat for each file
-        subindices = [(subindices,) for _ in filenames]
+    if isinstance(subindices, slice) or isinstance(subindices[0], int) or np.isscalar(subindices[0]):
+        # One set of subindices over time to repeat for each file
+        _subindices = [(cast(DimSubindices, subindices),) for _ in filenames]
 
-    elif isinstance(subindices[0], slice) or np.isscalar(subindices[0][0]):
+    elif isinstance(subindices[0], slice) or isinstance(subindices[0][0], int) or np.isscalar(subindices[0][0]):
         # Interpret this as being an iterable over dimensions to repeat for each file
-        subindices = [subindices for _ in filenames]
+        _subindices = [cast(FileSubindices, subindices) for _ in filenames]
 
     elif len(subindices) != len(filenames):
         # Must be a separate subindices for each file; must match number of files
-        raise Exception('Length of subindices does not match length of file list')        
+        raise Exception('Length of subindices does not match length of file list')
+    
+    else:
+        _subindices = cast(Sequence[FileSubindices], subindices)
+    del subindices  # ensure _subindices replaces subindices from here
 
     # Get the total size of the file
     all_shapes = [sbx_shape(file) for file in filenames]
-    all_shapes_out = np.stack([_get_output_shape(file, subind)[0] for (file, subind) in zip(filenames, subindices)])
+    all_shapes_out = np.stack([_get_output_shape(file, subind)[0] for (file, subind) in zip(filenames, _subindices)])
 
     # Check that X, Y, and Z are consistent
     for dimname, shapes in zip(('Y', 'X', 'Z'), all_shapes_out.T[1:]):
@@ -199,14 +203,15 @@ def sbx_chain_to_tif(filenames: list[str], fileout: str, subindices: Optional[Ch
     # Now convert each file
     tif_memmap = tifffile.memmap(fileout, series=0)
     offset = 0
-    for filename, subind, file_N in zip(filenames, subindices, all_n_frames_out):
-        _sbxread_helper(filename, subindices=subind, channel=channel, out=tif_memmap[offset:offset+file_N], plane=plane, chunk_size=chunk_size)
+    for filename, subind, file_N in zip(filenames, _subindices, all_n_frames_out):
+        this_memmap = cast(np.memmap, tif_memmap[offset:offset+file_N])
+        _sbxread_helper(filename, subindices=subind, channel=channel, out=this_memmap, plane=plane, chunk_size=chunk_size)
         offset += file_N
 
     del tif_memmap  # important to make sure file is closed (on Windows)
 
 
-def sbx_shape(filename: str, info: Optional[dict] = None) -> tuple[int, int, int, int, int]:
+def sbx_shape(filename: str, info: Optional[dict[str, Any]] = None) -> tuple[int, int, int, int, int]:
     """
     Args:
         filename: str
@@ -223,55 +228,41 @@ def sbx_shape(filename: str, info: Optional[dict] = None) -> tuple[int, int, int
 
     # Load info
     if info is None:
-        info = loadmat_sbx(filename + '.mat')['info']
+        info = loadmat_sbx(filename + '.mat')
 
     # Image size
     if 'sz' not in info:
         info['sz'] = np.array([512, 796])
-    
-    # Scan mode (0 indicates bidirectional)
-    if 'scanmode' in info and info['scanmode'] == 0:
-        info['recordsPerBuffer'] *= 2
 
     # Fold lines (multiple subframes per scan) - basically means the frames are smaller and
     # there are more of them than is reflected in the info file
     if 'fold_lines' in info and info['fold_lines'] > 0:
-        if info['recordsPerBuffer'] % info['fold_lines'] != 0:
+        if info['sz'][0] % info['fold_lines'] != 0:
             raise Exception('Non-integer folds per frame not supported')
-        n_folds = round(info['recordsPerBuffer'] / info['fold_lines'])
-        info['recordsPerBuffer'] = info['fold_lines']
+
         info['sz'][0] = info['fold_lines']
         if 'bytesPerBuffer' in info:
+            n_folds = round(info['sz'][0] / info['fold_lines'])
             info['bytesPerBuffer'] /= n_folds
-    else:
-        n_folds = 1   
+
 
     # Defining number of channels/size factor
     if 'chan' in info:
         info['nChan'] = info['chan']['nchan']
-        factor = 1  # should not be used
+    elif info['channels'] == 1:
+        info['nChan'] = 2
     else:
-        if info['channels'] == 1:
-            info['nChan'] = 2
-            factor = 1
-        elif info['channels'] == 2:
-            info['nChan'] = 1
-            factor = 2
-        elif info['channels'] == 3:
-            info['nChan'] = 1
-            factor = 2
+        info['nChan'] = 1
 
     # Determine number of frames in whole file
     filesize = os.path.getsize(filename + '.sbx')
     if 'scanbox_version' in info:
-        if info['scanbox_version'] == 2:
-            info['max_idx'] = filesize / info['recordsPerBuffer'] / info['sz'][1] * factor / 4 - 1
-        elif info['scanbox_version'] == 3:
+        if info['scanbox_version'] in [2, 3]:
             info['max_idx'] = filesize / np.prod(info['sz']) / info['nChan'] / 2 - 1
         else:
             raise Exception('Invalid Scanbox version')
     else:
-        info['max_idx'] = filesize / info['bytesPerBuffer'] * factor - 1
+        info['max_idx'] = filesize / info['bytesPerBuffer'] * (2 // info['nChan']) - 1
 
     n_frames = info['max_idx'] + 1    # Last frame
 
@@ -284,7 +275,7 @@ def sbx_shape(filename: str, info: Optional[dict] = None) -> tuple[int, int, int
         n_planes = 1
     n_frames //= n_planes
 
-    x = (int(info['nChan']), int(info['sz'][1]), int(info['recordsPerBuffer']), int(n_planes), int(n_frames))
+    x = (int(info['nChan']), int(info['sz'][1]), int(info['sz'][0]), int(n_planes), int(n_frames))
     return x
 
 
@@ -302,7 +293,7 @@ def sbx_meta_data(filename: str):
     if ext == '.sbx':
         filename = basename
     
-    info = loadmat_sbx(filename + '.mat')['info']
+    info = loadmat_sbx(filename + '.mat')
 
     meta_data = dict()
     n_chan, n_x, n_y, n_planes, n_frames = sbx_shape(filename, info)
@@ -400,13 +391,14 @@ def _sbxread_helper(filename: str, subindices: FileSubindices = slice(None), cha
         filename = basename
 
     # Normalize so subindices is a list over dimensions
-    if isinstance(subindices, slice) or np.isscalar(subindices[0]):
-        subindices = [subindices]
+    if isinstance(subindices, slice) or isinstance(subindices[0], int) or np.isscalar(subindices[0]):
+        _subindices = [cast(DimSubindices, subindices)]
     else:
-        subindices = list(subindices)
+        _subindices = list(cast(Sequence[DimSubindices], subindices))
+    del subindices  # ensure _subindices replaces subindices from here
 
     # Load info
-    info = loadmat_sbx(filename + '.mat')['info']
+    info = loadmat_sbx(filename + '.mat')
 
     # Get shape (and update info)
     data_shape = sbx_shape(filename, info)  # (chans, X, Y, Z, frames)
@@ -414,7 +406,7 @@ def _sbxread_helper(filename: str, subindices: FileSubindices = slice(None), cha
     is3D = n_planes > 1
 
     # Fill in missing dimensions in subindices
-    subindices += [slice(None) for _ in range(max(0, 3 + is3D - len(subindices)))]
+    _subindices += [slice(None) for _ in range(max(0, 3 + is3D - len(_subindices)))]
 
     if channel is None:
         if n_chans > 1:
@@ -430,7 +422,7 @@ def _sbxread_helper(filename: str, subindices: FileSubindices = slice(None), cha
     if frame_size <= 0:
         raise Exception('Invalid scanbox metadata')
 
-    save_shape, subindices = _get_output_shape(data_shape, subindices)
+    save_shape, _subindices = _get_output_shape(data_shape, _subindices)
     n_frames_out = save_shape[0]
     if plane is not None:
         if len(save_shape) < 4:
@@ -447,16 +439,18 @@ def _sbxread_helper(filename: str, subindices: FileSubindices = slice(None), cha
     if not is3D:  # squeeze out singleton plane dim
         sbx_mmap = sbx_mmap[..., 0]
     elif plane is not None:  # select plane relative to subindices
-        sbx_mmap = sbx_mmap[..., subindices[-1][plane]]
-        subindices = subindices[:-1]
-    inds = np.ix_(*subindices)
+        sbx_mmap = sbx_mmap[..., _subindices[-1][plane]]
+        _subindices = _subindices[:-1]
+    inds = np.ix_(*_subindices)
 
+    out_arr: Optional[np.ndarray] = out  # widen type
+    del out  # ensure out_arr replaces out from here
     if chunk_size is None:
         # load a contiguous block all at once
         chunk_size = n_frames_out
-    elif out is None:
+    elif out_arr is None:
         # Pre-allocate destination when loading in chunks
-        out = np.empty(save_shape, dtype=np.uint16)
+        out_arr = np.empty(save_shape, dtype=np.uint16)
 
     n_remaining = n_frames_out
     offset = 0
@@ -468,23 +462,26 @@ def _sbxread_helper(filename: str, subindices: FileSubindices = slice(None), cha
         # Note: SBX files store the values strangely, it's necessary to invert each uint16 value to get the correct ones
         np.invert(chunk, out=chunk)  # avoid copying, may be large
 
-        if out is None:
-            out = chunk  # avoid copying when loading all data
+        if out_arr is None:
+            out_arr = chunk  # avoid copying when loading all data
         else:
-            out[offset:offset+this_chunk_size] = chunk
+            out_arr[offset:offset+this_chunk_size] = chunk
         n_remaining -= this_chunk_size
         offset += this_chunk_size
 
+    if out_arr is None:
+        raise RuntimeError('Nothing loaded - no frames selected?')
+
     del sbx_mmap  # Important to close file (on Windows)
 
-    if isinstance(out, np.memmap):
-        out.flush()    
-    return out
+    if isinstance(out_arr, np.memmap):
+        out_arr.flush()    
+    return out_arr
 
 
-def _interpret_subindices(subindices: DimSubindices, dim_extent: int) -> tuple[Iterable[int], int]:
+def _interpret_subindices(subindices: DimSubindices, dim_extent: int) -> tuple[Sequence[int], int]:
     """
-    Given the extent of a dimension in the corresponding recording, obtain an iterable over subindices 
+    Given the extent of a dimension in the corresponding recording, obtain a sequence over subindices 
     and the step size (or 0 if the step size is not uniform).
     """
     logger = logging.getLogger("caiman")
@@ -507,15 +504,18 @@ def _interpret_subindices(subindices: DimSubindices, dim_extent: int) -> tuple[I
 
 
 def _get_output_shape(filename_or_shape: Union[str, tuple[int, ...]], subindices: FileSubindices
-                      ) -> tuple[tuple[int, ...], FileSubindices]:
+                      ) -> tuple[tuple[int, ...], tuple[Sequence[int], ...]]:
     """
     Helper to determine what shape will be loaded/saved given subindices
     Also returns back the subindices with slices transformed to ranges, for convenience
     """
     if isinstance(subindices, slice) or np.isscalar(subindices[0]):
-        subindices = (subindices,)
+        _subindices = (cast(DimSubindices, subindices),)
+    else:
+        _subindices = cast(Sequence[DimSubindices], subindices)
+    del subindices  # ensure _subindices replaces subindices from here
     
-    n_inds = len(subindices)  # number of dimensions that are indexed
+    n_inds = len(_subindices)  # number of dimensions that are indexed
 
     if isinstance(filename_or_shape, str):
         data_shape = sbx_shape(filename_or_shape)
@@ -529,7 +529,7 @@ def _get_output_shape(filename_or_shape: Union[str, tuple[int, ...]], subindices
     
     shape_out = [n_frames, n_y, n_x, n_planes] if is3D else [n_frames, n_y, n_x]
     subinds_out = []
-    for i, (dim, subind) in enumerate(zip(shape_out, subindices)):
+    for i, (dim, subind) in enumerate(zip(shape_out, _subindices)):
         iterable_elements = _interpret_subindices(subind, dim)[0]
         shape_out[i] = len(iterable_elements)
         subinds_out.append(iterable_elements)
diff --git a/testdata/2d_sbx_bidi.mat b/testdata/2d_sbx_bidi.mat
new file mode 100644
index 000000000..9eb119cda
Binary files /dev/null and b/testdata/2d_sbx_bidi.mat differ
diff --git a/testdata/2d_sbx_bidi.sbx b/testdata/2d_sbx_bidi.sbx
new file mode 100644
index 000000000..dfb220fe6
Binary files /dev/null and b/testdata/2d_sbx_bidi.sbx differ