ni-media

audio::ostream

The base class for all audio output streams.

unformatted output operations

Inherited from std::ostream

• write(): inserts blocks of characters

⚠️ Using these operations should be avoided. They are provided for maximum flexibility if clients need to operate on the raw pcm data. In most use cases, formatted output operations can and should be used as they provide type safety and are optimized for best performance.

positioning operations

Inherited from std::ostream.

• tellp(): returns the output position indicator
• seekp(): ⚠️ is not implemented yet. It is unclear at this point if this fucntionality can be / will be added later on, as it seems not all codecs support seeking while encoding.

⚠️ Using these operations should be avoided. They are provided for maximum flexibility if clients need to operate on the raw pcm data. It is the clients reponsibility to ensure that the position is aligned withing a sample or frame. Therefore it is recommended to use sample based positioning operations instead.

state functions

Inherited from std::basic_ios.

• good(): checks if no error has occurred i.e. I/O operations are available
• eof(): checks if end-of-file has been reached
• fail(): checks if an error has occurred
• bad(): checks if a non-recoverable error has occurred
• operator!(): checks if an error has occurred (synonym of fail())
• operator bool(): checks if no error has occurred (synonym of !fail())
• rdstate(): returns state flags
• setstate(): sets state flags
• clear(): modifies state flags

formatted output operations

These operations inserts one or more samples into the stream, by converting the sequence of samples to a pcm data sequence which is then insterted into the stream. The sample format can be any floating point type (i.e. float, double) or integral type (e.g int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t, uint32_t, uint64_t).

• operator<<: inserts samples into the stream.
  • The value-based operator inserts a single sample into the stream, in analogy to std::ostream operator<<.
  • The range-based operator inserts a range of samples into the stream.

⚠️ It is highly recommended to use the range-based version instead of the value-based version, as this will result in a better performance (during pcm conversion).

I.e. clients should stream block wise:

void fill(audio::ostream& stream, const std::vector<float>& samples)
{
    stream << samples;
}

rather than sample wise:

void fill(audio::istream& stream, const std::vector<float>& samples)
{
    for (auto sample : samples)
    {
        stream << sample;
    }
}

sample based positioning operations

• sample_tellp(): returns the output position indicator of the current sample.
• frame_tellp(): returns the output position indicator of the current frame.

audio specific operations

• info(): returns the stream info audio::ostream_info which contains audio specific information like:
  • num_channels: the number of channels
  • num_frames: the number of sample frames (one frame consist of num_channels samples)
  • sample_rate: the sample rate
  • format: the pcm format the audio data is stored in
  • …

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