I was able to create the exact error. The key seems to be,
2025:06:06-15:08:07 0x000018a0 [Info]: "[DownloadControlAmazon]" Selected SubtitleStream emtpy.
2025:06:06-15:08:07 0x000018a0 [Critical]: "[DownloadControlAmazon]" SelectSubtitleStream failed
as I stated before.
And that is because in Settings the following setting is set...
2025:06:07-08:47:47 0x00003e74 [Info]: [DRM Settings]: PreSelect Subtitle Language: QList()
which means it is set to None. That was the information I was missing. I had tried various languages and the download worked every time. I only got...
2025:06:07-08:54:25 0x00003e74 [Info]: CefControl::slotShowRemuxProgress "EDownloadType_Remuxing 100 / %2 "
2025:06:07-08:54:25 0x00003e74 [Info]: BatchDownloadManager::slot_setRecordResult " record result, id : B0DVH6RF6H, type : 3"
2025:06:07-08:54:25 0x00003e74 [Info]: [Download Check]: /************************************************** **************************/
2025:06:07-08:54:25 0x00003e74 [Info]: [Download Check]: download result: "failed"
2025:06:07-08:54:25 0x00003e74 [Info]: [Download Check]: fail code: 702
2025:06:07-08:54:25 0x00003e74 [Info]: [Download Check]: /************************************************** **************************/
when I used None in Settings for VIP Pre-select Subtitle Language along with all the other settings Bill2 uses (MP4, 720p, EAC3, etc.)
Germania, do you have None for Pre-select Subtitle Language? Or is the problem not in Germany?
As far as US Amazon and Bill2, he should be able to fix the 702 error (temporarily) by changing the setting from None to "Same as UI language", English, or any other language.
It appears that I was wrong in what I wrote about which program is used to remux MP4 files. MP4Box is known to cause 702 errors sometimes, but the logs show that FFmpeg is being used.
So, the big question is what, along with the None setting, is causing the 702 error. I normally use None all the time because I'm a USA-located English-speaker who rarely needs subtitles. But I don't use most of the other setting that Bill2 uses. @Wilson.Wang, the developer needs to figure out why the None setting and some other factor is causing 702 errors while remuxing with FFmpeg (possibly only when the "Video Format" is set to MP4.)