I have a react native app with expo go. The functionality is simple, I tap record, and then stop, and the audio file should be sent to Open AI and transcribe it to text.

However I am having difficulties as it requires a File, not an URI.

I get this error:

> ents/ExponentExperienceData/@levm38/ai-reminders/recording_1718887602296.mp3"}
> ERROR  Failed to transcribe audio: [AxiosError: Request failed with
> status code 400]  LOG  Response data: {"error": {"code": null,
> "message": "Invalid file format. Supported formats: ['flac', 'm4a',
> 'mp3', 'mp4', 'mpeg', 'mpga', 'oga', 'ogg', 'wav', 'webm']", "param":
> null, "type": "invalid_request_error"}}

The code is as follows:

  const stopRecording = async () => {
        console.log('Stopping recording...');
        setRecording(null);
        setIsRecording(false);
        await recording?.stopAndUnloadAsync();
    
        const uri = recording?.getURI();
        if (uri) {
          const timestamp = Date.now();
    
          try {
            // Convert recording to MP3
            const mp3FileUri = `${FileSystem.documentDirectory}recording_${timestamp}.mp3`;
            await FileSystem.copyAsync({
              from: uri,
              to: mp3FileUri,
            });
    
            console.log('Recording saved as MP3:', mp3FileUri);
    
            // Fetch duration of the recording
            const { sound } = await Audio.Sound.createAsync({ uri: mp3FileUri });
            const { durationMillis } = await sound.getStatusAsync();
            await sound.unloadAsync();
    
            await saveRecording(mp3FileUri, timestamp, durationMillis);
    
            // Read the MP3 file content into a Base64 string
            const mp3Base64String = await FileSystem.readAsStringAsync(mp3FileUri, {
              encoding: FileSystem.EncodingType.Base64,
            });
    
            // Convert Base64 string back to Blob
            const mp3Blob = await base64ToBlob(mp3Base64String, 'audio/mpeg');
    
            // Call the transcription function with the Blob object
            await transcribeAudio(mp3Blob);
          } catch (error) {
            console.error('Failed to save recording as MP3:', error);
          }
        }
      };
    
      const transcribeAudio = async (fileBlob) => {
        try {
          const formData = new FormData();
          formData.append('file', {
            uri: fileBlob.uri,
            type: 'audio/mpeg', // Set correct MIME type here
            name: `recording_${Date.now()}.mp3`, // Ensure the name is set appropriately
          });
          formData.append('model', 'whisper-1');
          formData.append('response_format', 'verbose_json');
          formData.append('timestamp_granularities', 'segment');
      
          const headers = {
            'Authorization': `Bearer ${openaiApiKey}`,
            'Content-Type': 'multipart/form-data',
          };
      
          const response = await axios.post('https://api.openai.com/v1/audio/transcriptions', formData, { headers });
          console.log('Transcription response:', response.data); // Log full response for debugging
      
          // Extract the actual transcription text from the response
          const transcriptionText = response.data.text;
          console.log('Transcription text:', transcriptionText);
        } catch (error) {
          console.error('Failed to transcribe audio:', error);
          if (error.response) {
            console.log('Response data:', error.response.data);
          }
        }
      };


const base64ToBlob = async (base64Data, contentType) => {
  console.log('Converting Base64 to Blob...');
  try {
    const response = await fetch(`data:${contentType};base64,${base64Data}`);
    const blob = await response.blob();
    console.log('Blob conversion successful:', blob);
    return blob;
  } catch (error) {
    console.error('Failed to convert Base64 to Blob:', error);
    throw error;
  }
};

If I check my logs I get this:

> LOG  Recording saved as MP3:
> file:///var/mobile/Containers/Data/Application/2C4F636D-9A6C-4FAD-976D-3A4D7D7B2EE7/Documents/ExponentExperienceData/@levm38/ai-reminders/recording_1718887873585.mp3
> LOG  Recording saved {"duration": 1858, "timestamp": 1718887873585,
> "uri":
> "file:///var/mobile/Containers/Data/Application/2C4F636D-9A6C-4FAD-976D-3A4D7D7B2EE7/Documents/ExponentExperienceData/@levm38/ai-reminders/recording_1718887873585.mp3"}
> LOG  Converting Base64 to Blob...  LOG  Blob conversion successful:
> {"_data": {"__collector": {}, "blobId":
> "92385B71-9F4F-4F40-9D2B-D09A84B06AF6", "name": "Unknown", "offset":
> 0, "size": 68915, "type": "audio/mpeg"}}  ERROR  Failed to transcribe
> audio: [AxiosError: Request failed with status code 400]  LOG 
> Response data: {"error": {"code": null, "message": "Invalid file
> format. Supported formats: ['flac', 'm4a', 'mp3', 'mp4', 'mpeg',
> 'mpga', 'oga', 'ogg', 'wav', 'webm']", "param": null, "type":
> "invalid_request_error"}}