issue #222: fix audio stream stutter btween ovelay TS file;

[suzp1984]

1. let continuity_counter continually between overlay ts;
2. copy audio data when transcoding ts;

[suzp1984]

This PR try to fix #222 .

Here is how I verify this PR.

Because I didn't has openAI account to run the whole process. I change the code first by remove the openAI api and render the ASR to video stream code, then I can reproduce same problem described in #222.

Then I add this PR, the issue disappear. So I guess this PR works. Send it to review and let others to verify on real env.