Lowering bitrate for HD-DVD and BluRay

[setarip_old]

I have converted some original, purchased HD-DVDs to, in one instance MKV and, in another, to a BluRay compliant MTS.

Is there a simple, fast way to reduce the bitrates of such files, so that they'll playback more smoothly on an underpowered, older system?

Thanks.

[PassThePeas]

You will have to re-encode to a lower bitrate (with x264 for instance, or use a tool as BD-Rebuilder (http://forum.doom9.org/showthread.php?t=143716)).
But if your cpu has trouble reading the original material, this should take some time (several hours, even maybe days). Maybe you should look into upgrading your cpu or getting a video card from wich you could use hardware acceleration.

[setarip_old]

this should take some time (several hours, even maybe days That's precisely what I'm trying to avoid (and why I've not yet used "BD Rebuilder" on this system) - while trying to get further utilization out of one of my older systems ;>}

[Dark Shikari]

I don't know of any transcoders for H.264 (reduce bitrate quickly without doing a full re-encode).

One thing you could do is do a full re-encode--but with extremely fast x264 settings. You can easily get realtime 1080p encoding in such a case, and faster settings could mean, for example, no CABAC and no loop filter, for much faster decoding as well.

You could also transcode to MPEG-2 using libavcodec, which is slightly faster than x264 on fastest settings.