I have FFmpeg installed on my linux web server. When I execute the following code, I have intermittent results.

I think I have figured out that the MP3s do not compile when they have different bitrates.

exec ('cat '. $pair['source_file'] . ' ' . $pair['translated_word_file'] . '>' . $temp_mp3);

I might have found some articles online that reference taking them apart and then bundling them back together at a consistent bitrates.

I have confirmed that this won't really work with basic "cat" function and that "sox" can be used IF they have the same sample rate.

The issue now becomes "What is the best way to get them to the same sample rate?"