TL;DR: we should check if there are new frames available to queue to the
ExternalTextureProcessor before actually queueing a frame.
The overall flow on the external texture processor:
- `SurfaceTexture.onFrameAvailable` is called on `ExtTexMgr`, and
- it calls `updateTexImage()`, and sets `frame`
- it calls `maybeQueueFrameToExtTexProc()`
- the frame is queued to `ExtTexProc` if `frame` is set
- From `ExtTexProc.queueInputFrame()`:
- notifies the `frameProcessorListener` of available frame
- notifies the `inputListener` of `onReadyToAcceptInputFrame`
- (`ExtTexMgr` is the listener), it calls `maybeQueueFrameToExtTexProc()`
again
-- Parallelly --
- `ExtTexProc` calls `inputListener.onInputFrameProcessed`, when the frame is
released
- (`ExtTexMgr` is the listener), sets `frame` to `null`
*Problem*
This logic relies on `frame` to be cleared at the right time.
In transformer, it's OK b/c `ExtTexProc` release the frame immediately in
`queueInputFrame()` and calls `onInputFrameProcessed` which also reset `frame`
But in previewing, the frame is not released for a while, up to 10 ms.
In this case, `frame` will not reset in this 10 ms, and
`maybeQueueFrameToExtTexProc()` is repeatedly queueing the same input frame.
PiperOrigin-RevId: 470211620
(cherry picked from commit a8c54dd3)
