Question: In EVS (Enhanced Voice Services) codec, how are non-received speech frames or frame-blocks between SID (Silence Insertion Description) frames during non-speech periods represented in stored files?
Option 1: As `SPEECH_LOST` frames to maintain synchronization.
Option 2: As `NO_DATA` frames to indicate absence of speech.
Option 3: By duplicating the last received speech frame.
Option 4: By inserting a series of zero-value bytes.
Explanation: During non-speech periods, if there are non-received speech frames or frame-blocks between SID frames, they are stored as `NO_DATA` frames. This approach efficiently indicates the absence of speech data without wasting storage on unnecessary filler content, unlike `SPEECH_LOST` which is used for frames lost during transmission to maintain synchronization with the original media stream.