WhatsApp has announced that it is working on a new audio chats update, as per a recent blog post in Wabetainfo. The update is under development and is expected to be rolled out for the WhatsApp beta for Android.
As per the screenshot, a new waveforms icon will be added to the chat header, allowing users to initiate audio chats. However, there is no official communication on how it will work.
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In the screenshot, there is a red button for ending ongoing calls, and there appears to be some additional space available. Since the waveform icon implies the capability of real-time audio visualisation, it is plausible that the space above the chat header could be reserved for displaying audio waveforms.