Transform from video_description modality to video_global_description modality.

[kdu4108]

Given data from:

video_description modality

root/video_description/shard-00000.tar
 |     ├── 00000.jsonl # this corresponds to one video. each line within it corresponds to one subsequence of frames.
 |     ├── 00001.jsonl
 |     └── ...

and the video_metadata modality

root/metadata/shard-00000.tar
 |     ├── 00000.json # this corresponds to one video.
 |     ├── 00001.json
 |     └── ...

and maybe video_transcript modality

root/video_transcript/shard-00000.tar
 |     ├── 00000.jsonl # this corresponds to one video. each line within it corresponds to one subsequence of frames.
 |     ├── 00001.jsonl
 |     └── ...

generate a global description (one string) for each video. The output format should look like

root/video_transcript/shard-00000.tar
 |     ├── 00000.txt # this corresponds to the global description for one video.
 |     ├── 00001.txt
 |     └── ...

And xxxxx.txt just looks contains a string, e.g.

This is a global description of a video!