[FFmpeg-user] Forced Subtitles Only

[petesea at frontier.com]

On Fri, 20 Feb 2015, Nicholas Robbins wrote:

> Let me know if it works. I only knew about it because I added it. I'm 
> glad someone else is using it too.

It looks like it works... at least in terms of adding only the forced 
subtitles.

But, there are a couple problems with the resulting video, in particular 
it's less then half the size of the original (6557837312 -> 2745004032) 
and the "bitrate" went from "6621 kb/s" in the original video down to 
"2771 kb/s" in the forced-subs copy.

I'm assuming some of that is because the original contains 5 audio streams 
and 9 subtitle streams and the copy only contains 1 audio stream and 1 
subtitle stream overlayed onto the video stream.  But it seems hard to 
believe removing 4 audio streams and 8 subtitle streams reduces the 
size/bitrate by that much.

The other problem is once it's transferred to my DVR it plays fine at 
normal speed, but if I fast forward, then stop, it skips ahead several 
minutes.  The original video (w/o subs) doesn't have this issue.

My goal is to add the hard/forced subs with as little change to the video 
stream as possible.   If something like this were possible, I'd do it:

   $ ffmpeg -forced_subs_only 1 -i video.vob -filter_complex "[0:v][0:s]overlay" -c copy -f vob video.mpg

I know I can't do that (I tried), just trying to emphasize I'd like the 
resulting video to be as close to the original as possible with the 
addition of the hard/forced subs.

If the video issues are unrelated to the overlay subtitle options and 
outside the scope of my current thread, I'll be glad to start a new 
thread.