encoding - 非标准采样率可以与 AAC 编码一起使用吗？

Question

我正在尝试将 M4a 文件从 41000 上采样到另一个非标准采样率，比如说 5000。

ffmpeg -i audio.wav -ar 5000 audio_.wav

无论对 m4a 不起作用，它对 wav 文件都能很好地工作。有什么想法吗？

如果非标准采样率不适用于 AAC，我需要任何文档或引用资料。

Answer 1

可用采样频率集受 AAC ADIF(音频数据交换格式)和 ADTS(音频数据传输流)限制。所以其他速率不能在 AAC 流中编码。以下是 ISO/IEC 13818-7 中 sampling_frequency_index 表单 8.1.1.2 的值标准:

关于@slhck 的回答

根据 ISO/IEC 13818-7 第 8.2.3 段:

8.2.3 Decoding Process

Assuming that the start of a raw_data_block() is known, it can be decoded without any additional „transport-level“ information and produces 1024 audio samples per output channel. The sampling rate of the audio signal, as specified by the sampling_frequency_index, may be specified in a program_config_element() or it may be implied in the specific application domain. In the latter case, the sampling_frequency_index must be deduced in order for the bitstream to be parsed.

Since a given sampling frequency is associated with only one sampling frequency table, and since maximum flexibility is desired in the range of possible sampling frequencies, the following Table shall be used to associate an implied sampling frequency with the desired sampling frequency dependent tables.

此表用于sampling_frequency_index推导。标准(ISO/IEC 13818-7 和 ISO/IEC 14496-3)暗示编码是使用这些固定频率之一进行的。