I am trying to download and merge video segments from a streaming service that provides video chunks as .tsa files (sometimes .tsb files). The site only gives me direct URLs to these .tsa segment files, each with a unique identifier and numbered sequentially (e.g., [unique-identifier]-0.tsa, [unique-identifier]-1.tsa, ... up to around 2k+ segments, lets say 2k).

Since the segments expire quickly and I do not have the original .m3u8 playlist URL to automate the download, I manually or via a script downloaded all segments by altering the URLs and saved each .tsa file locally.

{Earlier I used the copy the .m3u8 playlist link (from the inspect elements section), download the content using Jdownloader2; but now the new .m3u8 playlist links doesn't work. I get .tsa segments instead of .m3u8 links.
These are the new .m3u8 playlist links - https://[site]/[other-info]/[playlist-name]?quality=[in pixels]}

Because .tsa files are unrecognized by common tools, I renamed all .tsa files to .ts for compatibility, assuming they are just transport stream segments with a different extension.

I then created a file_list.txt for ffmpeg, listing all .ts segment filenames in sequential order, formatted like:
file '[unique-identifier]-0.ts'
file '[unique-identifier]-1.ts'
...
file '[unique-identifier]-2000.ts'

When I run the ffmpeg concat command:
ffmpeg -f concat -safe 0 -i file_list.txt -c copy output.mp4

I get errors such as:
"Impossible to open '[unique-identifier]-0.ts'"
"Invalid data found when processing input"

I confirmed all .ts segment files and the file list are located in the same directory. I suspect that these .tsa files are not standardized MPEG transport stream files and that renaming them to .ts is insufficient.

Attempts to probe or play the renamed .ts files failed, indicating that the .tsa files might be a proprietary or DRM-encoded streaming format.

I need guidance on:
1. How to convert or remux .tsa files properly to valid .ts or MPEG-TS segments usable by ffmpeg.
2. How to download these segments correctly, considering expiring URLs and necessary request headers.
3. How to use ffmpeg or other tools to merge all segments into a single playable video file without quality loss.