Subtitle Tagging & MP4's

[alhobart]

I am not sure if the issue I am having is a bug with Hybrid or a feature that is not supported by Hybrid or simply a problem with the MP4 container.  My issue is that I was trying to add 3 subtitles to an MP4 file.  I was able to add them, but the tag only gets written for the first subtitle and it shows up correctly ("English"), the other two ("French" and "Spanish") come out as "und" when trying to select a subtitle when the video is played on MPC-BE or VLC. The subtitles are there and work when selected, the problem is the tags that label subtitles two and three.  I have tried everything I can think of, many of them more than once.  The ironic part is that when I followed the exact same steps but changed the container I was saving it to, to a MKV file, the subtitles came out with the correct tags. 

I am running Windows 10, Hybrid version 2021.07.18.1, 64 bit. 

Here is my procedure:

Please note that the only change I made to the Config Tab was to select the Video and Audio Tags passthrough options under the Automation tab.

1) Load video file.
2) Set the output path and filename
2) Select the video and audio options
3) Select "Tagging" and "Subtitles"
4) Video and Audio are passthrough, so this ends the video and audio options
5) Go to the Subtitle Tab and load subtitle file into the Subtitle Queue
6) Go to Tagging Tab and select Streams
7) Go to the Subtitle tag and check the check mark for language and select the language
8) Click the arrow icon next to the language drop down menu to place it on the Tag Queue and confirm that it actually is in the Queue
9)  Repeat steps 5 - 8 for the next two subtitles
10) I next added chapters.
11) Go back to the "Base" tab and click the guy with the shovel. 
12) Wait until I get a notification that says it's done and then try the file to see if the tags on the subs showed up.

The above worked fine for the MKV file, but not for MP4.  Not a big deal when it comes to MKV vs. MP4, the frustrating part was that I wasted quite a bit of time before I decided to try a different container and it came out perfectly the first time.

Just for S&G, I tried to change the container from the successful MKV file back to an MP4, but I cannot figure out how to get the subtitles to passthrough.  The resulting MP4 comes out with no subtitles.  Oh, and I tried to mux in the subtitles one at a time, but like with the MKV to MP4 experiment, the original subtitle would get stripped out and only the one I was adding would end up with the resulting file.

Any thoughts on what I did wrong or what I need to look at are appreciated.

Thanks for your help.