I had the same problem as well when I first got the phone (FW 1.01) but it kinda fixed itself as I watched more videos. Happened to me again when I flashed to FW 1.03, I reinstalled the official Youtube app and it seems to be better now, although some videos can be choppy. Thanks for the suggestions of using a third party app, I will give that a go to see if it is better.
But every v3 has this problem or every mt6582 ?
Maybe i will sell mine and buy another one
I don't have any issue with youtube videos, even with HD enabled. But, with mx I can't watch videos with hardware decode, only with the software. There's no problem for me...
So far for videos, I've not faced any issues, both with YouTube or MX Player. I'm using this phone side by side with my Note II, and I can say the battery life is OK, considering I use them both about pretty even, the iNew in daily use will give me about 75% of what the Note II does, both lasts enough for me to be confidently autonomous for the day.
older version of youtube app works fine, install version 4.5 of official youtube app and there is no lag.
Viral app is great, i'm using it more than youtube app since i found out about it because of the playback feature
For easy access, i downloaded it and uploaded to my dropbox:
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I can confirm that it works properly.