Fix random_segment TypeError when duration_sec is a float

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What does this PR do ?

Fixes RandomSegmentPerturbation (random_segment augmentation) crashing with TypeError: pad_width must be of integral type. whenever it has to pad a short utterance and duration_sec is a float - including the constructor default 32.0.

Collection: ASR

Changelog

• nemo/collections/asr/parts/preprocessing/perturb.py: compute pad_size as math.ceil(self._duration_sec * data.sample_rate) - data.num_samples, an integer number of samples, so AudioSegment.pad -> numpy.pad always receives an integral pad_width. math.ceil rather than round/truncation is deliberate: the next statement is subsegment(0.0, duration_sec), which raises ValueError if the segment ends up shorter than duration_sec, so the padded length must not round down. The integer-duration_sec path is unchanged (math.ceil of an int is a no-op).
• tests/collections/asr/test_preprocessing_segment.py: new TestRandomSegmentPerturbation with parametrized duration_sec in [32.0, 32, 16.0, 16] verifying a short utterance is zero-padded to exactly int(duration_sec) * sample_rate samples for both int and float spellings.

Usage

import numpy as np
from nemo.collections.asr.parts.preprocessing.perturb import RandomSegmentPerturbation
from nemo.collections.asr.parts.preprocessing.segment import AudioSegment

seg = AudioSegment(np.zeros(16000 * 5, dtype=np.float32), 16000)  # 5 s of audio
p = RandomSegmentPerturbation(duration_sec=32.0, pad_to_duration=True)  # class defaults
p.perturb(seg)
print(len(seg.samples))  # 512000 (previously: TypeError)

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PR Type:

• New Feature
• Bugfix
• Documentation

Additional Information

• Related to random_segment augmentation raises TypeError: pad_width must be of integral type whenever it has to pad #16104
• This picks up fix(asr): pad random_segment with an integer sample count #16105 by @udsy19 (the issue reporter), which was closed unmerged by its author with an invitation for anyone to pick it up ("happy to reopen and rebase if anyone wants it picked up"). Same math.ceil approach.
• Scope note: random_segment augmentation raises TypeError: pad_width must be of integral type whenever it has to pad #16104 also flags that docs/source/asr/ssl/configs.rst omits pad_to_duration: true from its random_segment snippet; this PR fixes only the crash and intentionally leaves the docs change out (it was part of fix(asr): pad random_segment with an integer sample count #16105 if a maintainer wants it restored).
• Disclosure: this change was drafted with AI assistance; the author reviewed and tested it. DCO sign-off is on the commit.

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