I'm going to jump in here... I've experienced 2 of these phenomena primarily, and it has nothing to do with adobe screwing up.
Do any of you use OIS? Image stabilization I mean? I know what you are thinking... ..."Why would this idiot ask that?"
OIS will temporarily ALTER your framerate. This yields VFR video even if you set your camera for CFR. Some will actually speed up the frame rate, and just drop frames to compensate, but others will simply drop motioned frames and place a reference that's supposed to clue in an encoder to build a new one. I've had some panasonic OIS really screw up the frame rate when importing. IF you fall into this mess, and you want to get out of it, start with transcoded video\audio that's uncompressed. I know most people say just stick to mp4 or the MTS\AVCHD from the camera, but this can yield a VFR frame rate with OIS and it can be disastrous. Premiere doesn't play back your source through an engine, it builds a preview for you to play back when you render. It's heavily dependent on source frames (its an analog style editing mechanism; it doesn't guess frames for you, it's not an encoder). WMM and others are totally Digital, and outputting from them only outputs a new file with the OIS handled (guessed frames are built and stored in the stream). Recode the video. It's the only real fix; and you should do it with uncompressed video if you want to retain quality.
The other instance is an old ID-10-T problem I've run across in many different workflows... I'll get to the counteract in just a moment...
I have encoded my video in the past using compressed source (directly from the camera), which was slow and clunky when adding effects, so I decided to move to intermediate codecs or uncompressed codecs. I found that doing so allows for better video speed, and fully renders out the OIS guess frames, removing the other issue. One problem tackled.
Now I've got a new one... ...One video codes just fine and plays perfectly outside premiere... But inside... ...Jumpy and the audio is out of sync. Hmmmmmm... Turns out that ProRes, AVI and other uncompressed codecs will use hardcoded values for audio (in other words, they will hardcode the sample rates into the file and lock it to that speed). When importing to Premiere, everything is fine, until you place it in a sequence. Try playing the source video in the source monitor (not in a sequence, remove it completely from all sequences). If it plays back okay, then your problem is that your sequences DO NOT MATCH YOUR HARDCODED AUDIO in your main source file. I was dropping 96k down to 48k. No wonder... I'm playing half the audio speed. "But mister, all the audio shows up in the sequence..." Doesn't matter. It will play your 96k audio at 48k, exactly half it's speed or it will drop audio frames at a rate that doesn't match the video properly.
Two main workarounds exist... ...1. You can try using the Milliseconds setting, which should conform the audio to time rather than sample, and time should code to Time just fine, but I haven't tried it (it's a theoretical).
The fix I use has 2 variants: Make the carpet match the drapes... ...eh, make the source audio match the sequence, or make the sequence match the source. Can you see how this has two variants? The easiest is to make the sequence match the audio, as you could simply create a new sequence, and drag-drop your edits from one sequence to the other, fixing your problem if you already have edits. The other option is to render out an audio file from your source or use your uncompressed file to render out an audio file that matches your sequence, then place it in the second audio layer, turning off the first. Try playing it. IF it still has sync problems, you may have other OIS issues, where some frames were not properly guessed when you encoded. See the following:
If you have AV files with sync problems that show only in premiere, you can force the files to guess. I've found the After Effects rendering engine to provide the best output in this instance. It will follow strict instruction sets, and will guess the frames if you set a constant frame rate. If you are already uncompressed this will go even faster. I've had better success going from 30p to 60i, as this guessed the fields and made more guesses of less data per guess. Some don't like interlaced video, so go ahead and render your progressives. Make sure you set the frame rate and all the rest for your COMP. This will conform the comp to the video. You should even be able to use your direct source (from the camera). Adobe will read and decompress it through after effects much better than media encoder, even though media encoder is a full encoder engine. Why? AME processes the frames with less strict algorithms (motion video algorithms), where AE uses image rendering of the frames when uncompressing (each frame is an image, so it processes the image, which will force a guess of missing or damaged frames).
I know I may not have a perfect answer for you here, but I hope I've given you some idea of where the problem lies. I've faced this twice. Originally I thought it was my hardware slowdown, but I rendered out part of the sequence to an output file, and it was still awful. I worked backward through each stage to find the issue. If playback outside the editor, or even in the basic source monitor is fine, but skewed in the sequence, the problem is your sequence settings aren't matching up properly. By checking that against your source, you can then narrow it down. If your source plays back everywhere just fine and gives you only one frame rate setting (i.e. 29.97), that doesn't tell you anything about whether or not the frames are fully articulated or guessed. It only tells you how fast it plays the frames. IF it notes a CFR or VFR, then you're usually clued in. Now you have to go back to your source hardware: the camera. IF the video was given to you by a client, you may not know where the files came from or how they were shot. Pass it through AE and set the frame rate constant. This will fix any guesses at the frame level. If you have the camera, check the ois capabilities. All OIS in digital is a "guessing" form of interpolation, even non active. If you set it to active, it should fix on it's own by passing through AE. IF you set it to non Active, you will get VFR in some areas of your video, and you may have to change your frame rate to fix the problem; so again use AE to cut it down. For this last instance, remember that quality will be degraded, but with plugins and some tweaking, you can get a decent output that doesn't hurt your pride, or your workmanship.
Just remember: ITS NOT PREMIERE'S FAULT. It's an editor that focuses on whole frames, conforms all to a constant rate so your timecode is always standard (i.e. you don't have to guess how fast things are moving, and you don't have to suddenly change time codes in the middle of the edit).
One other workaround that *might* work is using FRAMES instead of a drop frame timecode in a sequence. This will allow the sequence to speed up or down with a VFR video. Again, your sequence isn't matching your video if you have a VFR but are editing in CFR. It's not the fault of the program. You might also try right click source and "Create Sequence from clip", but I'm not sure that will solve anything either. If you set the timecode to frames, you will only play those frames at a specified frame rate. The only way to fix that would be to chop up the video into clips of 1s, and conform the frames to each clip.
Again, premiere editing is based on FRAMES, not SECONDS. If you could set both audio and video to milliseconds you might be able to keep sync with VFR, but premiere is a STANDARD based program. It was made to be able to go down to the frame level at all times. Other editors vary their markets, and provide results that are varied as well. Premiere has a specific target output. Go with high quality, standard input and you'll get higher quality, standardized output. For consumer grade work, standards are important as they remove some of the decisions that take time away from editing. Start by encoding your video to a set standard, and pass it through a rendering engine that has strict adherence. When that's done, edit away, frame by frame, with all the power and control you can get, without the needs of higher end processing power.
Premiere was made to work in a VARIETY of environments! My intel core 2 duo 2.16ghz 4gbram 256mbvidram can run it just fine. It has trouble with final cut, AVID, and even freeware unix tools. They have to process a lot more in real time to get VFR frames to work properly.
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