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joel jackson
h264 and wmv playback errors
on Jun 1, 2010 at 9:35:42 pm

All of my encodes WMV and h264 are chocking on playback and are malfunctioning when trying to scrub, ff, or rew in both quicktime player and wmv player. Clients are experiencing the same problem. I've never had this problem in the past and both of my macs running snow leopard experience the problem with the playback. I have also tried encoding from both systems with the same results. Movies encoded as h264 directly from quicktime player7 do not exhibit the same playback problems. Being on mac I have not tested this on the windows media encoder with .wmv files but I assume it would be the same results as encoding directly through quicktime. Has anyone experienced this problem and if so what was done to correct it?

Thanks,
Joel

Joel Jackson
http://www.creativebloc.com/port.html


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Craig Seeman
Re: h264 and wmv playback errors
on Jun 1, 2010 at 9:44:16 pm

Without more details I can only guess but maybe you need to increase the Keyframe rate (frequency). Try doing a keyframe every 5 seconds (150 frames NTSC) and set it to both Natural and Forced keyframes. You are using Episode 5.3.2 aren't you?



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joel jackson
Re: h264 and wmv playback errors
on Jun 1, 2010 at 9:53:48 pm

crap! I totally had it set to natural kf only. Encoding 101 for idiots (me being the idiot of course)!

Thanks,
Joel

Joel Jackson
http://www.creativebloc.com/port.html


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ryan loetscher
Re: h264 and wmv playback errors
on Jul 30, 2010 at 4:01:21 pm

Aren't those artifacts due to the way you set your IDR frames? Unless every I-frame is an IDR frame you'll get artifacts when you scrub. I thought I read that open GOP structures can cause that problem too because the predictive frames are using frames outside of the keyframe sequence... though that one I'm not 100% on.



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Craig Seeman
Re: h264 and wmv playback errors
on Jul 30, 2010 at 4:36:11 pm

That can be a reason if it's an Open GOP and there are others as well.
The nature of GOP means each non key frame must be constructed in real time. B frames are harder than P frames which are harder than I frames. The number of reference frames can have impact as well as that's the degree the decoder (player) has to look both forward and back to construct the frame. Entropy CAVLC vs CABAC has impact too.

All the above is also impacted by the player and the hardware its running on. Settings for easier decode can also have costs in quality/efficiency. It's the grand juggle every compressionist must make.

BTW this is one of the things that makes H.264 different than other codecs. There's a decoder spec but there's lots of encoder flexibility. That's why there's one VP6 and it's by On2. With H.264 you have Dicas, Main Concept, x264, Apple, Matrox MAX and several others. The better H.264 encoder codec implementations give you a lot of control but with that comes the responsibility of understanding what all the settings do and how they interact. It's why Apple's H.264 is so simple and also extremely inefficient compared to Episode. People who think Apple's H.264 looks great don't understand the cost. It's highly inefficient on the encode and decode side. Some will spot this on lower bit rates. Some note how slow the encoding is because is has to do so many passes. All its encodes are CAVLC although CABAC is more efficient (and slightly harder to decode). BTW one can stretch to all those inexpensive compression apps that "just work." There's major cost in that "just work" and the cost is inefficiency. Yes driving a well designed race car does take a bit more effort on the part of the driver than driving a go cart.

Sorry for tangential response but I do thing it's important to understand what makes Episode the excellent sports care it is and why you might bump into challenges and the thinking one needs to drive it with speed and finesse.



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