How to play multiple wav files with minimal delay?

[dingetje]

I'm using your library to play wav files stored on an SD_MMC file system to generate a simple TTS system.

bool play_file(char *filename, int volume)
{
  Serial.println("play_file: '" + String(filename) + "'");
  if (!SD_MMC.exists(filename)) {
    Serial.println("play_file: '" + String(filename) + "' does not exist");
    return false;
  }
  es8311_voice_volume_set(es_handle, volume, NULL);
  audio.connecttoFS(SD_MMC,filename);
  return true;
}

void SoundLoop()
{
  if (audio.isRunning())
  {
      audio.loop();
      vTaskDelay(1);
      return;
  }
  // next file in the vector?
  if (!fileVector.empty())
  {
    // pop next filename from the playlist
    String fileName = fileVector.front();
    fileVector.erase(fileVector.begin());
    play_file((char*)fileName.c_str(),DEFAULT_VOICE_VOLUME);
  }
}

/* add a file to the audio queue, file already checked for existance on SD */
void add_file(char* filePath)
{
  fileVector.push_back(String(filePath));
}

While this works, there's a noticable delay between each audio file.
I suspect this is caused by the load time of the next file, but I have no idea how to improve this.