Video Sequence Editor: playback lag after stripchange I got some footage from a band who played playback on a stage for a music video. Now I am putting it all together in VSE with the audiofile (studio recording) they used for playback. 

My machine is usually quite capable of handling FullHD video (GTX 970, 32 GB Ram, i7 4790K), but this time the video playback during editing starts to lag as hell when the current frame enters a new strip. That's quite annoying, since these transitions are the parts I am most interested in.

Here an example - to the left of the green marker: smooth 25 FPS playback. Once entering the second stip - image stops for more than 1 second and continues stuttering (not very helpful) playback afterwards. It basically skips the middle strip completely during playback.



Some notes, which may help encircle the problem:


I remember a "Prefetch Frames" setting, which should preload a certain number of frames into memory. For some reason, this has vanished in 2.79. 
The Memory Cache Limit in User Preferences -> System is set to 16000, so I don't expect this to be a problem.
I guessed that blender is trying to load something from harddisk - but when I look at the Windows Resource Monitor and filter for "blender.exe", it shows no hard disk activities.
The files I am working with are quite long (4-5 Min), and I only am interested in sub-sequences in the second half. Maybe this is some codec-video seeking issue!?
Speaking of codecs: I have files with .mov and .mp4 endings. According to the tool MediaInfo, the .mov is a MPEG-4 (Quicktime) Container with an AVC (High@L4.1)(CABAC/2 Ref Frames) video stream and the .mp4 files are MPEG-4 (Base Media) containers with AVC (High@L5.1)(CABAC/16 Ref Frames) video streams. 
I am using soft cuts (K and not shift-K).
In the movie clip editor, there is a purple stipe at the bottom of the screen, which shows how much frames are loaded already. At least I understood it like that. Example below. Probably this is what's happening in the VSE in my case - not loaded frames. But there is no similar visual feedback for the user in the VSE. Right?!



Any suggestions to ensure smooth playback WITHOUT using proxies are highly appreciated. I would like to avoid the overhead of generating temporary files or re-converting the footage to other codecs.
Encode your video files with post-production codec.

First thing you should look at is what a video codec you use. Every codec has a different use. In fact, most codecs that compress the video stream are only for linear playback.

So when you try to use codec what designed just for playing in videoplayer, it can be slow in non-linear playback. If you need fast workflow, use a special post-production codec. In blender good variant is a Avid DNxHD codec. Also you can try Apple ProRes  

Unlike other programs, in the blender you must process the source material  manually (if necessary). If you use another application, you will see, that most other programs will re-encode the video before adding it to the editing line. In this there are pluses and minuses, but this is so. 

Therefore, you still need to transcode the video, but next time you will encode into the right format. If you use files, that are not optimized to work in the video editor, there are no ways to make the workflow fast.