8Mbps + Stills = Macroblocks

[daamon]

Hi,

I have some short DV AVI clips (from my DV cam) of various super cars and Formula 1 cars whizzing by on demo runs.

I also have a load of 1600 x 1200 JPEG stills pictures.

I've combined both the video footage and the stills in Adobe Premiere 6.0 and I'm frameserving the finished project (video only) using the PluginPac FrameServer to TMPGEnc.

Because the total time is short enough, I'm using CBR @ 8,000 kbps - my logic being that the stills won't present any problems and the fast motion of the cars (and some fairly serious hand wobble coz I had to hold the camera over people's heads) would benefit from the high bitrate.

Here's the problem - The fast motion scenes are just fine, it's the stills (or some of them). They get the occasional appearance of blocks - either one square or a whole row of them. Some are artifacts of the previous still, some are just bright colours (pinks and greens mostly).

Sometimes, there's the odd group of blocks that are actually a part of the still picture but in the wrong place.

I tried lowering the bitrate to 6,000 kbps and it improved the blocks on the stills (though not completely removing them, but close enough), but I noticed some compromise on the fast scenes.

I tried ticking the "No motion search for still picture part by half pixel" on the "Quantize Matrix" tab in the settings - this helped with the blocks but made the stills look more pixelated ("blocky"), less defined. This was at both 7,000 and 8,000 kbps.

Any ideas? Thanks...

[Forum Troll]

Did you try usung the 2-pass VBR setting?

[daamon]

Hi Forum Troll,

That's my next line of attack - I avoided it as it takes well over an hour to encode a 16 minute clip, compared to about 45 mins with CBR. To my mind CBR should work unless there's some logical reason why 8Mbps screws up stills. Anyone?

But, if it does the job... I'm gonna set it off when I'm done replying. I'll report back.

Cheers.

[petar]

TMPGEnc in my experience is not very good at encoding stills (though it's a very good encoder). In fact, any authoring tool I've tried did a better job at encoding stills than TMPGEnc.

Try inserting an I picture manually (under GOP structure/Force picture type setting) for your stills.

Another thing you can try is convert the stills to DV before importing in Premiere (you can do this with Windows Movie Maker).

I would have approached your task differently though (I assume you're making a DVD). I'd encode the DV on its own (or in parts, if your stills go in between scenes) and then let the authoring tool encode the stills. All authoring tools are normally OK for this job. Then, depending on how capable your authoring tool is, you can arrange your clips/stills whichever way you want and set the playing time for the stills to whatever you want.

[flaninacupboard]

i second the motion to insert I frames manually, TMPGenc isn't always great at this.
Where do you have your motion search precision set?

[daamon]

Try inserting an I picture manually (under GOP structure/Force picture type setting) for your stills.

Wow - I hadn't even thought of looking at that. Not only would it be useful for stills, but being able to set specific frames as an "I picture" would mean much better chapter selection. Thank you...

i second the motion to insert I frames manually, TMPGenc isn't always great at this.
Where do you have your motion search precision set?

Hi flan. How's things? My first instincts were that I couldn't select a range of frames (that'd be handy!!!) as there are quite a few stills each running for 4 - 6 seconds = a LOT of frames. But then I saw you can load a list - it's a simple text file with the simple format frame num,I, e.g. 234,I - easily done in Excel for a range and copy / paste into notepad.
Motion search = "High quality (slow)" - because of the fast moving cars.

Another thing you can try is convert the stills to DV before importing in Premiere (you can do this with Windows Movie Maker).

I can import the stills into Premiere and export as DV AVI that way. My only problam is that there's transitions from motion to stills back to motion. But something to remember for future needs...

As it turns out, it looks like encoding using 2-pass VBR (max 8,500 average 6,000 and min 500) has done the job.

So, problem solved - it seems like TMPGEnc doesn't like encoding stills. 2-pass VBR is one of the ways around it, but exporting the stills to DV AVI would (I guess) also work too.

Thanks all...