Fix #2867

[Whning0513]

Fix #2867

问题描述

使用 torchaudio.load() 加载某些 MP3 文件时返回空 tensor。

根因分析

在 torchaudio/_backend/soundfile_backend.py 的 load 函数中，第 222 行存在 dtype 判断逻辑缺陷：

with soundfile.SoundFile(filepath, "r") as file_:
    if file_.format != "WAV" or normalize:
        dtype = "float32"       # <-- 这里硬编码为 float32

当 soundfile.SoundFile 以 "r" 模式打开 MP3 文件时，由于 format != "WAV"，代码进入该分支并将 dtype 硬编码为 "float32"。然而，某些 MP3 文件使用 DOUBLE 编码格式，其 data 段需要 float64 精度才能正确读取。使用 float32 读取此类文件会导致返回空 tensor 或数据丢失。

修复方案

在 float32 降级之前，先检查文件实际的 subtype：

subtype_dtype = _SUBTYPE2DTYPE.get(file_.subtype)
if subtype_dtype in ("float64",):
    dtype = "float64"
else:
    dtype = "float32"

修改后逻辑

• 非 WAV 格式（MP3/FLAC/OGG 等）且 normalize=True：

  • 如果文件 subtype 为 "DOUBLE"，则使用 "float64" 读取，避免精度损失
  • 如果 subtype 为 "FLOAT" 或其他整形类型，则使用 "float32" 读取（即原行为）

• WAV 格式且 normalize=True：与上述逻辑一致，会自动处理 DOUBLE 类型的 WAV 文件

• WAV 格式且 normalize=False：使用原始整数类型读取（行为不变）

修改文件

• torchaudio/_backend/soundfile_backend.py（或 torchaudio/backend/soundfile_backend.py 包装器指向的实际后端文件）

涉及行

load() 函数中第 222 行附近（if file_.format != "WAV" or normalize: 分支）。

[pytorch-bot]

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