Notices

I also want to mention that 400x240 is the correct aspect ratio for the tablet's screen (1.66 or 16:10) , so it fills the whole screen and looks really good.

640x352 is 1.8 aspect ratio (close to widescreen cinema) not the tablet's aspect ratio, and so it fills less of the screen. (640 * 1.25 = 800, 352 * 1.25 = 440, not 480).

I'd be interested to see you compare apples to apples here. Please crop the width of your video from 640 to 576 and re-encode. It is still not perfect, because it is hard to find numbers that "fit" the tablet's aspect ratio in that range and also meet the "must be divisible by 16" rule that many mp4 players most mp4 encoders require... (EDIT: thanks sjgadsby!)

Ain't got no QuickTimePro here; just right-clicked link in Post #15, saved-as (to my Windows machine) and double-clicked. Maybe you need to clear cache before you try again?

I don't know how I missed that post. There's an hour I'd like back. Thanks to all.

I tried 2 passes again in 640x352, same video.

- At 650 Kbps, plays smooth
- At 800 Kbps jerky on high motion scenes

The divisible by 16 rule isn't an arbitrary choice made by player manufacturers, it's due to the codecs involved. More specifically, it is because the codecs use discrete cosine transformations for spacial compression. Because color channels are subsampled at 4:2:0, their 8x8 blocks actually represent 16x16 areas in the image. So, you get 16x16 macroblocks.

MPEG-4 Part 10 supports other block sizes, if I recall correctly, but I don't know that they provide the same compression efficiency.

Qole, i just respected the ratio of my original video.

I generally prefer having black bands above and under the picture than to crop it and loose a significant part of the image to fill the screen ... For me the reference is the source's ratio, not the screen ...

But it's a matter of taste, i fought a lot with my boyfriend when we had a 82 cm tube TV ... he even used a special mode that stretch the 4:3 picture mainly on the right and left sides ... to fill the screen !!! Soooooo baaaad !!!

totololo: I understand that you're using the original aspect ratio.

But those black bands can affect performance. That's why I wanted to "compare apples to apples" and have you crop your video.

I always crop to the tablet's screen size because a big 4.3" screen full of vibrant video is always a real shock-and-awe experience for people. Especially computer animated kids movies -- they tend to be bigger, brighter and more in-your-face.

PS: I agree with you about stretching 4:3 video to fit a wide screen. That's just WRONG.

Qole, my video doesn'have black bands in it, it's the player that add very thin black bands up and down ... do you think it can degrade performance ? OOOOOH, i will try it !

No, actually, I think the black bands probably are improving performance. The more "unused" screen space that you have, the better the performance.

That's why I'd like to see you crop 5% (32 px) off of both sides of your video; the video will then fill the screen and we can see how high you can push the bitrate with full screen video.

Qole, I tested it :
576x352 (small cropping on both sides)
2 passes
700Kbps

And it runs very well !
The picture is gorgeous, vibrant, full of details. It's even more amazing than with the small black bands up and down.

Except when everything moves very fast : mosaïc, but i find it acceptable, because it's a trailer, it moves a lot more than in the real movie (trailers always are quite epileptic don't you think ?).