Chat Streaming doesn't work with audio modalities

[vbandi]

Bug Report

Overview

The gpt-4o-audio-preview-2024-12-17 model allows for audio as an output modality. This doesn't seem to work.

To Reproduce

Steps to reproduce the behavior:

The code below doesn't have any Delta or any data in the chunks.

async Task GPTSpeech()
{
    var client = new OpenAIClient();
    var speaker = new SpeakerOutput();

    var chatRequest = new ChatRequest([new Message(Role.System, "Count from 1 to 10. Whisper please")],
        audioConfig: new AudioConfig(Voice.Nova), model: "gpt-4o-audio-preview-2024-12-17");  // Doesn't seem to work... OpenAI Lib issue??
        
    await foreach (var chunk in client.ChatEndpoint.StreamCompletionEnumerableAsync(chatRequest))
    {
        if (chunk.FirstChoice.Delta is not null)
            Console.Write(chunk.FirstChoice.Delta.Content);

        if (chunk.FirstChoice.Message?.AudioOutput is not null)
            Console.WriteLine(chunk.FirstChoice.Message.AudioOutput.Data.Length);
    }

    Console.WriteLine("Done.");
    Console.ReadKey();

}

However, when not providing audio in the ChatRequest, this still works:

    var chatRequest = new ChatRequest([new Message(Role.System, "Count from 1 to 10. Whisper please")]);

Expected behavior

Chunks should contain text and / or audio content when the model is generating audio

[StephenHodgson]

Ended up being broken for both async and Enumerable streaming paths.