Watching the outputTemp folder, where the program assembles the downloaded streams, one of the first temporary files that the program creates is "0." in the Sub_00 folder (subfolder of Period_00, which is a subfolder of a temporary folder under the temporary Amazon folder). This "0." file is the subtitles in TTML format. With "Extract Original Format" selected, during the remux stage it is copied to a file named st_00.ttml in the same temporary folder. Unfortunately, it is deleted with the rest of the temporary files instead of being moved to the permanent output folder (but if Subtitle Only is the download option, it is copied to the permanent output folder). So the program has no trouble extracting the subtitles from Amazon in TTML format. To remux them into the MP4 file, it needs to convert the TTML file to an SRT file. That's the step that fails. The "convert result subtitle" routine is invoked 3 times and fails each time. The error message says "transformXmlToSrtSubtitle failed". With a zero-length or nonexistent SRT file, the RemuxMultiAudioSrtMetadataUtil call, which appears to be a wrapper around FFMPEG.EXE, is called without a subtitle input stream.
2024:06:08-09:29:39 0x00003010 [Info]: convert result subtitle file d:%5CM%5C_IN%5CTEMP/outputTemp/Amazon/2024_06_08_09_26_55_B0CH8X4FKG/Period_00/Sub_00/st_00.srt is exist? : 0, file size is 0
2024:06:08-09:29:39 0x00003010 [Critical]: "[DownloadControlAmazon]" transformXmlToSrtSubtitle failed, retry
2024:06:08-09:29:39 0x00003010 [Info]: convert result subtitle file d:%5CM%5C_IN%5CTEMP/outputTemp/Amazon/2024_06_08_09_26_55_B0CH8X4FKG/Period_00/Sub_00/st_00.srt is exist? : 0, file size is 0
2024:06:08-09:29:39 0x00003010 [Critical]: "[DownloadControlAmazon]" transformXmlToSrtSubtitle failed, retry
2024:06:08-09:29:39 0x00003010 [Info]: convert result subtitle file d:%5CM%5C_IN%5CTEMP/outputTemp/Amazon/2024_06_08_09_26_55_B0CH8X4FKG/Period_00/Sub_00/st_00.srt is exist? : 0, file size is 0
2024:06:08-09:29:39 0x00003010 [Critical]: "[DownloadControlAmazon]" transformXmlToSrtSubtitle failed, retry
2024:06:08-09:29:39 0x00003010 [Info]: Subtitle done.
2024:06:08-09:29:39 0x00003010 [Info]: [DownloadControlAmazon]" "remuxDownloadedFiles subtitle stream, langCode :eng, path :D:\\M\\_IN\\TEMP/outputTemp/Amazon/2024_06_08_09_26_55_B0CH8X4FKG/Period_00/Sub_00/st_00.srt, bForced :0