[Q] MP4 concatenation with Video PassThroughTrackStrategy does nothing

Maybe I misunderstood how this library works, but if I try to merge 2 mp4 files that are exactly the same, I assumed a PassThroughTrackStrategy would be enough and it would merge the 2 video files together. However when I do

```
Transcoder.into(output.fileDescriptor)
.addDataSource(context, uri1)
.addDataSource(context, uri2) // uri1 and uri2 are a copy of the same mp4 file
.setVideoTrackStrategy(PassThroughTrackStrategy())
.transcode()
```

I just get `Validator has decided that the input is fine and transcoding is not necessary.`.

I was expecting this, but I would have expected to merging to take place. However the final output file is completely empty.

Is this expected behaviour, and if so Is there a way to make this work without a full video transcoding?

Thanks!