The compress data size is bigger than the original pcm data?

Hello,everyone:
Our product use flac codec for serveal years,it worked well.Now we notice that some times the compress data data size is bigger than the original pcm data,we are very confused. Is it the compress data absolutely has less size than the original pcm data,if not, what is the maximum size of the compress data.

Here is the details:
1. Our flac version is 1,3,3
2. frame size is 1024 samples,that is we encode 1024 samples one time.
3. other parameters are: 2 channels, int16 format,set compression to 5; sample rate is 48000.
4.We use FLAC__stream_encoder_init_stream api and set the write_callback function.
use FLAC__stream_encoder_process_interleaved api for encode,and in the write callback function to get the compress data and size.
5. our raw pcm data size is 4096 bytes (for 2 channel,int16 format).but some times the compress data is a little bigger than 4096.
6. kylin os

Thanks in advance.

Start with the FLAC__stream_encoder_init_stream and FLAC__stream_encoder_process_interleaved entry points, then inspect how the write_callback receives encoded data for the stated frame and format parameters. Compare the reported 4096-byte PCM input with the callback output and determine whether the size increase is expected; done means the behavior and maximum size question are answered clearly.