On large projects (I am working on a 30 minute short with about 250 Gigs of DNxHD video data) Blender uses to get unresponsive in some cases:
1. After working on one sector of the timeline for a short time, e.g. minute 15 to 17, when I move to an other one, for example the beginning, and press play, on each cut the playback stutters. I think because each clip has to be reloaded in some way. Somehow other NLEs can manage this more efficient but I don't know how this works exactly, sorry.
2. On that a large project, after inserting a bigger video file into the timeline and immediately moving the timeline cursor around, the UI gets stuck for a few seconds. That does not happen with huge video files in small projects.
3. Often pressing play or ALT+A does not work. Blender shows that it is playing back the animation by displaying the "Anim Player" button in the header, but gets stuck. Then you have to press stop and start several times again to get the playback work.
I cannot attach a blend file because the project size on which those problems occur exceeds the upload limit.
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There're couple of limitations in how blender's sequencer is working would prevent from working with large files.
Mainly it's a seek inside the sequence. It could be slow if you're not using timecodes. Using timecode would likely resolve scrubbing slowdown you're mentioning. This slowdown could be caused by something else, but it's difficult to say for sure without having particular file which has issues.
Stutters are caused by the fact that when time cursor goes to another strip it opens FFmpeg context, which could be slow for some files. If this happens on every time cursor goes form one strip to another it'll be needed to have sample blend and video files which gives the issue.
I'm not sure what exactly it means blender stuck on playback, having sample would really help here.
So far it sounds you're run into limitation of sequencer design, it could be improved to work better for larger projects, but that wouldn't be considered a bug.
Okay, I see. Yes, those Stutters while playback between clips are only appearing in passages that have not been played for some time so that the context has to be loaded again. That is clear for me now, thanks.
With blender getting stuck on playback I mean that when I press Alt+A or the play button nothing happens sometimes except that the stop animation player button appears in the sequencer window's header. The Cursor does not move and no Playback happens. I have to wait a moment, stop the playback and start it again to make it work.
I think that this happens randomly. I was not able to figure out any condition to trigger it yet.
I do not want to post any unnecessary bugs as most problems with the sequencer seem to be well known though there are no bug reports for the most. So is it already known that the sequencer cache ignores the memory cache limit from the user settings and buffers all frames until the ram is full in the recent revisions since a change to the buffer was committed some weeks ago? Also that blenders ram usage increases continuously while rendering sequences (for the 30 minute project I needed about 20 GB)?