VSE - Playback lags and slows down at cuts

Support Compositing and Post Processing
#1

I’m trying to cut quite a view videos together. In general, i really like the workspace you can create with blender and the VSE, I basically have everything I could wish for. Unfortunately the playback is very slow and laggy, and I have no idea why.

The facts:

  • 8GB Ram, 4GB for Blender
  • Intel i5 3450
  • Crucial M4 SSD
  • 19 (at least) Videos at once loaded into VSE-Projekt
  • Videos are movs (29.97 FPS, H264, MPEG4 AVC, 1920x1080; PCM, 48kHz, 16 Bits)
  • Videos range from 700MB to 1.6GB
  • I use one reference audio track for the videos (wav, PCM S16 LE, 44.1khz, 16 Bits)
  • I want to cut all these Videos into litte snippets, fitting the audio

As I said, the workspace is great, but the playback is very laggy. AV-Sync is activated. Encoding is H264 (although this doesn’t seem to affect performance at all).

Playback is fine when there are not cuts (well, sometimes it lags a bit when you move the playback-cursor around, but not bad). As soon as Blender touches cuts (I use soft cuts) the video starts lagging, often for several seconds. Audio keeps going normally. It’s practically not possible to work like this :confused: .
This also happens when removing all but one movie in VSE.

What am I doing wrong here?

#2

First I would suggest rendering and editing with proxies. But if you must stay with original videos (due to size restrictions on HDD) try increasing VSE Strip properties panel > Strip Input > MPEG Preseek: (greater than zero) e.g. 10frames

This should enable blender to peak ahead for the next edit. Also try increasing the User Prefs > Sequencer > Memory Cache Limit.

But honestly I wouldn’t expect much performance increase from Blender as it is not a modern optimised NLE. It prefers frame sequences to stream, as they don’t tax the system with decoding like H264 etc.

#3

Thank you.

I realized this, so i created some small proxys myself. Now everything works perfectly.

Still a bit disappointed though. But, as you said, Blender is not optimized for this usecase, and I should be happy with what I get from this free software.

I have one further question: I just tried rendering the video in high quality (1920x1080, H264, 29.97 FPS). Unfortunately this messes up my keyframes, especially certain video effects are out of sync or broken. Rendering in low Quality (960x540) produces a correct video.
It seems, that Blender gets out of sync when my computer has to work a lot. Is there anything I can do, do fix this (besides upgrading my hardware…)?