Add implementation of `spectrogram_batch` (#27159)

* Add initial implementation of `spectrogram_batch`

* Format the initial implementation

* Add test suite for the `spectrogram_batch`

* Update `spectrogram_batch` to ensure compatibility with test suite

* Update `spectrogram_batch` to include pre and post-processing

* Add `amplitude_to_db_batch` function and associated tests

* Add `power_to_db_batch` function and associated tests

* Reimplement the test suite for `spectrogram_batch`

* Fix errors in `spectrogram_batch`

* Add the function annotation for `spectrogram_batch`

* Address code quality

* Re-add `test_chroma_equivalence` function

* Update src/transformers/audio_utils.py
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Update src/transformers/audio_utils.py
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

---------
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

src/transformers/audio_utils.py

@@ -18,7 +18,7 @@ and remove unnecessary dependencies.
 """
 
 import warnings
-from typing import Optional, Tuple, Union
+from typing import List, Optional, Tuple, Union
 
 import numpy as np
 
@@ -581,6 +581,213 @@ def spectrogram(
     return spectrogram
 
 
+def spectrogram_batch(
+    waveform_list: List[np.ndarray],
+    window: np.ndarray,
+    frame_length: int,
+    hop_length: int,
+    fft_length: Optional[int] = None,
+    power: Optional[float] = 1.0,
+    center: bool = True,
+    pad_mode: str = "reflect",
+    onesided: bool = True,
+    preemphasis: Optional[float] = None,
+    mel_filters: Optional[np.ndarray] = None,
+    mel_floor: float = 1e-10,
+    log_mel: Optional[str] = None,
+    reference: float = 1.0,
+    min_value: float = 1e-10,
+    db_range: Optional[float] = None,
+    remove_dc_offset: Optional[bool] = None,
+    dtype: np.dtype = np.float32,
+) -> List[np.ndarray]:
+    """
+    Calculates spectrograms for a list of waveforms using the Short-Time Fourier Transform, optimized for batch processing.
+    This function extends the capabilities of the `spectrogram` function to handle multiple waveforms efficiently by leveraging broadcasting.
+
+    It supports generating various types of spectrograms:
+
+        - amplitude spectrogram (`power = 1.0`)
+        - power spectrogram (`power = 2.0`)
+        - complex-valued spectrogram (`power = None`)
+        - log spectrogram (use `log_mel` argument)
+        - mel spectrogram (provide `mel_filters`)
+        - log-mel spectrogram (provide `mel_filters` and `log_mel`)
+
+    How this works:
+
+        1. The input waveform is split into frames of size `frame_length` that are partially overlapping by `frame_length
+            - hop_length` samples.
+        2. Each frame is multiplied by the window and placed into a buffer of size `fft_length`.
+        3. The DFT is taken of each windowed frame.
+        4. The results are stacked into a spectrogram.
+
+    We make a distinction between the following "blocks" of sample data, each of which may have a different lengths:
+
+      - The analysis frame. This is the size of the time slices that the input waveform is split into.
+      - The window. Each analysis frame is multiplied by the window to avoid spectral leakage.
+      - The FFT input buffer. The length of this determines how many frequency bins are in the spectrogram.
+
+    In this implementation, the window is assumed to be zero-padded to have the same size as the analysis frame. A
+    padded window can be obtained from `window_function()`. The FFT input buffer may be larger than the analysis frame,
+    typically the next power of two.
+
+    Note: This function is designed for efficient batch processing of multiple waveforms but retains compatibility with individual waveform processing methods like `librosa.stft`.
+
+    Args:
+        waveform_list (`List[np.ndarray]` with arrays of shape `(length,)`):
+            The list of input waveforms, each a single-channel (mono) signal.
+        window (`np.ndarray` of shape `(frame_length,)`):
+            The windowing function to apply, including zero-padding if necessary.
+        frame_length (`int`):
+            The length of each frame for analysis.
+        hop_length (`int`):
+            The step size between successive frames.
+        fft_length (`int`, *optional*):
+            The size of the FFT buffer, defining frequency bin resolution.
+        power (`float`, *optional*, defaults to 1.0):
+            Determines the type of spectrogram: 1.0 for amplitude, 2.0 for power, None for complex.
+        center (`bool`, *optional*, defaults to `True`):
+            Whether to center-pad the waveform frames.
+        pad_mode (`str`, *optional*, defaults to `"reflect"`):
+            The padding strategy when `center` is `True`.
+        onesided (`bool`, *optional*, defaults to `True`):
+            If True, returns a one-sided spectrogram for real input signals.
+        preemphasis (`float`, *optional*):
+            Applies a pre-emphasis filter to each frame.
+        mel_filters (`np.ndarray`, *optional*):
+            Mel filter bank for converting to mel spectrogram.
+        mel_floor (`float`, *optional*, defaults to 1e-10):
+            Floor value for mel spectrogram to avoid log(0).
+        log_mel (`str`, *optional*):
+            Specifies log scaling strategy; options are None, "log", "log10", "dB".
+        reference (`float`, *optional*, defaults to 1.0):
+            Reference value for dB conversion in log_mel.
+        min_value (`float`, °optional*, defaults to 1e-10):
+            Minimum floor value for log scale conversions.
+        db_range (`float`, *optional*):
+            Dynamic range for dB scale spectrograms.
+        remove_dc_offset (`bool`, *optional*):
+            Whether to remove the DC offset from each frame.
+        dtype (`np.dtype`, *optional*, defaults to `np.float32`):
+            Data type of the output spectrogram.
+
+    Returns:
+        List[`np.ndarray`]: A list of spectrogram arrays, one for each input waveform.
+    """
+    window_length = len(window)
+
+    if fft_length is None:
+        fft_length = frame_length
+
+    if frame_length > fft_length:
+        raise ValueError(f"frame_length ({frame_length}) may not be larger than fft_length ({fft_length})")
+
+    if window_length != frame_length:
+        raise ValueError(f"Length of the window ({window_length}) must equal frame_length ({frame_length})")
+
+    if hop_length <= 0:
+        raise ValueError("hop_length must be greater than zero")
+
+    # Check the dimensions of the waveform
+    for waveform in waveform_list:
+        if waveform.ndim != 1:
+            raise ValueError(f"Input waveform must have only one dimension, shape is {waveform.shape}")
+
+    # Check if waveform is complex
+    for waveform in waveform_list:
+        if np.iscomplexobj(waveform):
+            raise ValueError("Complex-valued input waveforms are not currently supported")
+
+    # Center pad the waveform
+    if center:
+        padding = [(int(frame_length // 2), int(frame_length // 2))]
+        waveform_list = [
+            np.pad(
+                waveform,
+                padding,
+                mode=pad_mode,
+            )
+            for waveform in waveform_list
+        ]
+    original_waveform_lengths = [
+        len(waveform) for waveform in waveform_list
+    ]  # these lengths will be used to remove padding later
+
+    # Batch pad the waveform
+    max_length = max(original_waveform_lengths)
+    padded_waveform_batch = np.array(
+        [
+            np.pad(waveform, (0, max_length - len(waveform)), mode="constant", constant_values=0)
+            for waveform in waveform_list
+        ],
+        dtype=dtype,
+    )
+
+    # Promote to float64, since np.fft uses float64 internally
+    padded_waveform_batch = padded_waveform_batch.astype(np.float64)
+    window = window.astype(np.float64)
+
+    # Split waveform into frames of frame_length size
+    num_frames = int(1 + np.floor((padded_waveform_batch.shape[1] - frame_length) / hop_length))
+    # these lengths will be used to remove padding later
+    true_num_frames = [int(1 + np.floor((length - frame_length) / hop_length)) for length in original_waveform_lengths]
+    num_batches = padded_waveform_batch.shape[0]
+
+    num_frequency_bins = (fft_length // 2) + 1 if onesided else fft_length
+    spectrogram = np.empty((num_batches, num_frames, num_frequency_bins), dtype=np.complex64)
+
+    # rfft is faster than fft
+    fft_func = np.fft.rfft if onesided else np.fft.fft
+    buffer = np.zeros((num_batches, fft_length))
+
+    for frame_idx in range(num_frames):
+        timestep = frame_idx * hop_length
+        buffer[:, :frame_length] = padded_waveform_batch[:, timestep : timestep + frame_length]
+
+        if remove_dc_offset:
+            buffer[:, :frame_length] -= buffer[:, :frame_length].mean(axis=1, keepdims=True)
+
+        if preemphasis is not None:
+            buffer[:, 1:frame_length] -= preemphasis * buffer[:, : frame_length - 1]
+            buffer[:, 0] *= 1 - preemphasis
+
+        buffer[:, :frame_length] *= window
+
+        spectrogram[:, frame_idx] = fft_func(buffer)
+
+    # Note: ** is much faster than np.power
+    if power is not None:
+        spectrogram = np.abs(spectrogram, dtype=np.float64) ** power
+
+    # Apply mel filters if provided
+    if mel_filters is not None:
+        result = np.tensordot(spectrogram, mel_filters.T, axes=([2], [1]))
+        spectrogram = np.maximum(mel_floor, result)
+
+    # Convert to log scale if specified
+    if power is not None and log_mel is not None:
+        if log_mel == "log":
+            spectrogram = np.log(spectrogram)
+        elif log_mel == "log10":
+            spectrogram = np.log10(spectrogram)
+        elif log_mel == "dB":
+            if power == 1.0:
+                spectrogram = amplitude_to_db_batch(spectrogram, reference, min_value, db_range)
+            elif power == 2.0:
+                spectrogram = power_to_db_batch(spectrogram, reference, min_value, db_range)
+            else:
+                raise ValueError(f"Cannot use log_mel option '{log_mel}' with power {power}")
+        else:
+            raise ValueError(f"Unknown log_mel option: {log_mel}")
+
+        spectrogram = np.asarray(spectrogram, dtype)
+
+    spectrogram_list = [spectrogram[i, : true_num_frames[i], :].T for i in range(len(true_num_frames))]
+
+    return spectrogram_list
+
+
 def power_to_db(
     spectrogram: np.ndarray,
     reference: float = 1.0,
@@ -632,6 +839,55 @@ def power_to_db(
     return spectrogram
 
 
+def power_to_db_batch(
+    spectrogram: np.ndarray,
+    reference: float = 1.0,
+    min_value: float = 1e-10,
+    db_range: Optional[float] = None,
+) -> np.ndarray:
+    """
+    Converts a batch of power spectrograms to the decibel scale. This computes `10 * log10(spectrogram / reference)`,
+    using basic logarithm properties for numerical stability.
+
+    This function supports batch processing, where each item in the batch is an individual power (mel) spectrogram.
+
+    Args:
+        spectrogram (`np.ndarray`):
+            The input batch of power (mel) spectrograms. Expected shape is (batch_size, *spectrogram_shape).
+            Note that a power spectrogram has the amplitudes squared!
+        reference (`float`, *optional*, defaults to 1.0):
+            Sets the input spectrogram value that corresponds to 0 dB. For example, use `np.max(spectrogram)` to set
+            the loudest part to 0 dB. Must be greater than zero.
+        min_value (`float`, *optional*, defaults to `1e-10`):
+            The spectrogram will be clipped to this minimum value before conversion to decibels, to avoid taking
+            `log(0)`. The default of `1e-10` corresponds to a minimum of -100 dB. Must be greater than zero.
+        db_range (`float`, *optional*):
+            Sets the maximum dynamic range in decibels. For example, if `db_range = 80`, the difference between the
+            peak value and the smallest value will never be more than 80 dB. Must be greater than zero.
+
+    Returns:
+        `np.ndarray`: the batch of spectrograms in decibels
+    """
+    if reference <= 0.0:
+        raise ValueError("reference must be greater than zero")
+    if min_value <= 0.0:
+        raise ValueError("min_value must be greater than zero")
+
+    reference = max(min_value, reference)
+
+    spectrogram = np.clip(spectrogram, a_min=min_value, a_max=None)
+    spectrogram = 10.0 * (np.log10(spectrogram) - np.log10(reference))
+
+    if db_range is not None:
+        if db_range <= 0.0:
+            raise ValueError("db_range must be greater than zero")
+        # Apply db_range clipping per batch item
+        max_values = spectrogram.max(axis=(1, 2), keepdims=True)
+        spectrogram = np.clip(spectrogram, a_min=max_values - db_range, a_max=None)
+
+    return spectrogram
+
+
 def amplitude_to_db(
     spectrogram: np.ndarray,
     reference: float = 1.0,
@@ -681,6 +937,51 @@ def amplitude_to_db(
     return spectrogram
 
 
+def amplitude_to_db_batch(
+    spectrogram: np.ndarray, reference: float = 1.0, min_value: float = 1e-5, db_range: Optional[float] = None
+) -> np.ndarray:
+    """
+    Converts a batch of amplitude spectrograms to the decibel scale. This computes `20 * log10(spectrogram / reference)`,
+    using basic logarithm properties for numerical stability.
+
+    The function supports batch processing, where each item in the batch is an individual amplitude (mel) spectrogram.
+
+    Args:
+        spectrogram (`np.ndarray`):
+            The input batch of amplitude (mel) spectrograms. Expected shape is (batch_size, *spectrogram_shape).
+        reference (`float`, *optional*, defaults to 1.0):
+            Sets the input spectrogram value that corresponds to 0 dB. For example, use `np.max(spectrogram)` to set
+            the loudest part to 0 dB. Must be greater than zero.
+        min_value (`float`, *optional*, defaults to `1e-5`):
+            The spectrogram will be clipped to this minimum value before conversion to decibels, to avoid taking
+            `log(0)`. The default of `1e-5` corresponds to a minimum of -100 dB. Must be greater than zero.
+        db_range (`float`, *optional*):
+            Sets the maximum dynamic range in decibels. For example, if `db_range = 80`, the difference between the
+            peak value and the smallest value will never be more than 80 dB. Must be greater than zero.
+
+    Returns:
+        `np.ndarray`: the batch of spectrograms in decibels
+    """
+    if reference <= 0.0:
+        raise ValueError("reference must be greater than zero")
+    if min_value <= 0.0:
+        raise ValueError("min_value must be greater than zero")
+
+    reference = max(min_value, reference)
+
+    spectrogram = np.clip(spectrogram, a_min=min_value, a_max=None)
+    spectrogram = 20.0 * (np.log10(spectrogram) - np.log10(reference))
+
+    if db_range is not None:
+        if db_range <= 0.0:
+            raise ValueError("db_range must be greater than zero")
+        # Apply db_range clipping per batch item
+        max_values = spectrogram.max(axis=(1, 2), keepdims=True)
+        spectrogram = np.clip(spectrogram, a_min=max_values - db_range, a_max=None)
+
+    return spectrogram
+
+
 ### deprecated functions below this line ###