Mobile Encoding

[Lele-brz]

Hi,
I have some questions about encoding in H.264 for mobile devices.
I know that different mobiles have different screen res, codec support and so on, I'm just trying to define some general rules.

1. Having to use low bitrate (for network streaming), let's say around 220 kbps, what kind of screen resolution I should keep?
2. If for instance a device has a screen res of 320x240 would it make sense to use a higher res for encoding a video (ex: 640x480)
3. For preserving battery life what settings I should use? I would use a custom Baseline but maybe there can be some additional tweaking.

Thanks in advance
Bye

[Comatose]

1. It really depends on the type of content. A good way to tell would be to use CRF mode and find the quality your eyes like, then see the average bitrate for that, and then you can make compromises by reducing the resolution, modifying the video to make it easier to compress (e.g. blurring) or just decide that the compression artifacts at a lower bitrate aren't severe enough to warrant doing any of that.
2. Not really. There are no clear benefits, and some devices can't do resizing. What's more, it will take more processing power to decode, and processing power is something mobile devices are generally short of.
3. I don't really know, and honestly I don't think you should bother. It would be very hard to test the effect, and most devices restrict the settings to deal with their battery life/available processing power already, so...

[cogman]

as comatose said,

1. for quality, bitrate really varies from video to video. There is no good rule of thumb. CRF is your safest bet if quality is a concern.

2. Higher resolutions only benefit devices that can play them. Other then that they will just eat up the bitrate and force more processing power to be needed. If you are working with a small screen always resize to the resolution of that screen (Even consider half resolution)

3. The only way to really conserver battery power would be to use the least processor intensive encoding options. Even then, there is no guarantee that will give you a second more playback time. You should be more worried about using settings that work with your device rather then preserving its battery life, as there are many that can't playback H.264.

Mobile encoding are a very finicky thing. If you can avoid them, do. Other then that, look up posts on this forum that give details on how to playback H.264 files on the different devices. There are many threads on the more common devices (PsP)

[Lele-brz]

Thanks both for answering,
For the devices I'm considering I think using a QVGA(320x240) with 250 kbps h264 should be ok for all of them.
I was just wondering then why some devices with a screen res of 480x320 support video with res up to 640x480.

[Comatose]

Probably for "bigger is better". And maybe for compatibility with already encoded videos, but I doubt it since you usually have to re-encode anyway.

[Lele-brz]

So, for example for a 1280x720 (16:9) what would be the most appropriate resolution for a device (let's say Iphone) that has a screen res of 480x320 ?

I was thinking 512x288, but that means that it will be resized and I have additional pixels on Width, it's not a problem because it plays fine, I'm just thinking at the optimal resolution to choose.

[Comatose]

I would say 480x270 padded with black borders to 360 (unless the device supports automatically adding them, in which case you should go for 480x272 for mod16ness)

512x288 is kinda pointless since it's going to get downsized to 480x270 anyway.