Missing audio on output video after FFmpeg overlay

[Seangottarun]

Issue

As mentioned in #5 (review), when the GPS data video is overlayed on the original input video, the audio stream is dropped. According to ffmpeg-python documentation,

Some ffmpeg filters drop audio streams, and care must be taken to preserve the audio in the final output. The .audio and .video operators can be used to reference the audio/video portions of a stream so that they can be processed separately and then re-combined later in the pipeline. This dilemma is intrinsic to ffmpeg, and ffmpeg-python tries to stay out of the way while users may refer to the official ffmpeg documentation as to why certain filters drop audio.

TODO

• Find proper way to keep audio stream without distortion or any modification
• Test on Windows and macOS