Bluetooth bandwidth limits, video streaming...?

Ok so I cant really reveal to many details of where these questions come from, but I was interested in having a discussion on BT tech.

Basically I am working on a new product to allow for low power completely portable media transport from a number of sources. Now most mobile phones do not have the ability to create a wifi hotspot, but all have onboard bluetooth. Also most laptops these days also have BT support built in.

So according to the whitepapers BT3/4 have a limit of 24mbps transfer speed. While not a slouch by any means it certainly isnt blisteringly fast either.

So where I am at lets say due to low battery or just interference our device in question is only maintaining a 16mbps link. Assuming a maximum display size of 720P this leaves us with a bit of a quandry. Is this sufficient bandwidth to pass a minimally encoded/compressed video stream? Or is the smarter route to stress both devices a bit higher by forcing the host/server unit to do a high compression encoding on the stream and then also crank up the strain on the client device forcing to decode this compressed stream??

Ideally anything I can do to reduce overhead on the client side unit is preferable as it should improve battery life, and also reduce hardware cost on this unit. However, lower power usage at the cost of reliability of signal is absolutely not acceptable.

Opinions?

ssjwizard said:

Ok so I cant really reveal to many details of where these questions come from, but I was interested in having a discussion on BT tech.

Basically I am working on a new product to allow for low power completely portable media transport from a number of sources. Now most mobile phones do not have the ability to create a wifi hotspot, but all have onboard bluetooth. Also most laptops these days also have BT support built in.

So according to the whitepapers BT3/4 have a limit of 24mbps transfer speed. While not a slouch by any means it certainly isnt blisteringly fast either.

So where I am at lets say due to low battery or just interference our device in question is only maintaining a 16mbps link. Assuming a maximum display size of 720P this leaves us with a bit of a quandry. Is this sufficient bandwidth to pass a minimally encoded/compressed video stream? Or is the smarter route to stress both devices a bit higher by forcing the host/server unit to do a high compression encoding on the stream and then also crank up the strain on the client device forcing to decode this compressed stream??

Ideally anything I can do to reduce overhead on the client side unit is preferable as it should improve battery life, and also reduce hardware cost on this unit. However, lower power usage at the cost of reliability of signal is absolutely not acceptable.

Opinions?

Click to expand...

Is this true?

trents said:

Is this true?

Click to expand...

I suppose I should be more specific about that statement. Most mobile phones AS SHIPPED cannot create a wifi network. If you root your phone there are plenty of options, but by default out of the box most do not have this capacity. Further it is also worth noting that hosting a wifi hotspot on your mobile eats alot more battery than a simple BT connection.

You may be correct. My Motorola Droid Turbo 2 has hot spot ability and I think my previous phone, the HTC One did. And my wife's Samsing Galaxie 6 does. A lot of them do I believe. But I'm sure you are correct about the battery usage. That certainly makes sense.

Hm... My grandparents have 3Mbps internet and I have no problem streaming 720p video over there. So Bluetooth should be fine as well I'm guessing?

On another note, isn't Bluetooth what smart televisions use when you broadcast something from your phone, let's say a YouTube video, to the TV? If so, this product wouldn't be too different from that concept would it?

Vishera said:

Hm... My grandparents have 3Mbps internet and I have no problem streaming 720p video over there. So Bluetooth should be fine as well I'm guessing?

On another note, isn't Bluetooth what smart televisions use when you broadcast something from your phone, let's say a YouTube video, to the TV? If so, this product wouldn't be too different from today concept would it?

Click to expand...

TV thing: no. Not usually. It's using either the built in wifi on the TV or network port depending on how it is connected. Some may use wifi direct, but I don't think many do.

Vishera said:

Hm... My grandparents have 3Mbps internet and I have no problem streaming 720p video over there. So Bluetooth should be fine as well I'm guessing?

Click to expand...

There is a big difference between uncompressed and compressed video in terms of processing power required to decode. More processing power required = more power used/faster battery drain and higher hardware cost to build.

An average blueray is encoded at ~40mbps for 1080P. Knock that down to 720P and its around 30mbps instead. DVDs average bitrate is between 5-7mbps. To run 720P at 3mbps your going to run into 2 issues here. 1: quality loss, and 2: compression/decompression CPU load.

With a limit of say 12mbps it may be possible to employ a lightweight compression scheme to get that 30mbps down to around 12-15, but I can only think of two codecs that can do that effectively without substantial loss of quality and both are heavy hitters when it comes to CPU load levels. Furthermore not only does this increase the load on the client end, but also on the server end. I think that streaming at 480P and up-scaling may reduce the overall CPU load, but probably suffers from equal or greater quality loss.

MPEG-2 is the standard of choice for low processing decode, but has the largest file size. Stripping the bitrate down from 40mbps to 12mbps in MPEG-2 at 720P probably has sufficient quality loss that it honestly cant be considered HD anymore.
H.264 is the high quality compression of choice, but also has one of the most complex and CPU loading decode processes tied to it. Admittedly I may be able to find a low power CPU/GPU SOCs that has hardware level support for H.264, but whether or not the power consumption benefit outweighs that hardware cost is a whole nother component to the equation that I have not quite worked out yet.

Without knowing the actual use scenario, I would suggest considering the actual quality needed at the displaying device. Not focusing on the resolution alone, how big is the display? Presumably you want some "good enough" quality there. It may be possible 1080p with higher compression could look better than 720p with lower compression, to give comparable data rates.

Also with bluetooth, I'm not up to speed on all the possible variations of all the versions these days, but will range be a possible consideration? Whatever codec you choose, you probably want to plan for packet loss even at short range. If it isn't latency sensitive, you can make use of retransmission with buffering, otherwise you'll have to consider loss concealment.

Depending on the number of devices you want to run in a small area, you may also run into density problems, especially if the area already has heavy 2.4 GHz wifi usage.

Wifi Direct is supported in Android 4.0 and above.
https://developer.android.com/guide/topics/connectivity/wifip2p.html
The new Raspberry Pi Zero W would probably be a great fit for your application. It has a low power GPU capable of 1080p decode and built in Wifi.