I placed the microphone icon in prompt-form.tsx (https://github.com/vercel/ai-chatbot/blob/main/components/prompt-form.tsx)
<div className="relative flex flex-col w-full px-8 overflow-hidden max-h-60 grow bg-background sm:rounded-md sm:border sm:px-12">
{/* Flex container for buttons */}
<div className="absolute top-4 left-0 sm:left-4 flex items-center space-x-2">
{/* Tooltip for New Chat button */}
<Tooltip>
<TooltipTrigger asChild>
<button
onClick={e => {
e.preventDefault();
router.refresh();
router.push('/');
}}
className={cn(
buttonVariants({ size: 'sm', variant: 'outline' }),
'rounded-full bg-background p-0'
)}
>
<IconPlus />
<span className="sr-only">New Chat</span>
</button>
</TooltipTrigger>
<TooltipContent>New Chat</TooltipContent>
</Tooltip>
{/* Microphone component */}
<Microphone onTranscription={(transcription) => setInput(transcription)} />
</div>
The microphone component is an exact copy of microphone.tsx from the Nextjs starter, and route.ts is also the same.