Some readers may be familiar with my recent look at freeview, but for those who aren’t, I was basically interested in finding out how much data is in the air for digital TV, and how much data is dedicated for each service, noting the quality implications of variety vs quality.
What some readers may not know is that I’m an avid Satellite TV enthusiast and wild-feed hunter as well. I decided to deploy a very similar methodology to my Freeview analysis towards the Foxtel Satellite Services occupying Optus C1/D3 at 156 degrees East in order to catalogue the available services and their measured bit-rates.
NOTE: None of the following data will, in any way, shape or form, help anybody gain access to Foxtel. In fact, I don’t have access to Foxtel, and thanks to the use of NDS and Irdeto in conjunction with CSA, it is highly unlikely that anyone besides legitimate subscribers will have access to Foxtel services.
However, as the broadcasts are in standard DVB-S/DVB-S2 format, the metadata describing the broadcast is all “in the clear” and an analysis based on metadata is presented here.
The reception equipment is my venerable (now almost 2.5 years old) TBS TBS6925 Professional DVB-S2 Satellite Card (which I have nothing but praise for and will review in a later blog posting).
It is important to note that all of the measured bit-rates are “measured” with a degree of error, and the extensive use of statistical multiplexing leads to the continual shuffling of bit-rates between channels on each transponder. All of the measurements are “snapshot” one-time measurements made on the afternoon of Saturday 5th October 2013 – and as usual, satellite services are subject (and prone to) change in order to keep with current content line-ups and balance transponder loading.
Transponders and Modulation Modes
Foxtel presently utilizes a total of 26 carriers of about 37Mhz bandwidth on both Optus C1 and Optus D3 satellites co-located in the 156 degrees E slot. There are four DVB-S2 carriers using 8PSK for HD services, the rest being the older DVB-S standard QPSK transmissions. The 8PSK services transmit with pilots ON and a more conservative modulation mode to compensate for the increased demands of phase-noise stability on the LNB.
The bandwidth occupied by the carrier and the payload bandwidth were calculated based on the calculator provided at satellite-calculations.com and can vary slightly from what you can get using other calculation methods.
The total purchased bandwidth appears to be about 972.936Mhz, which, given the Optus D1/D2/D3 payload information of each transponder being 54Mhz wide, and each satellite carrying 24 Ku band transponders, means that Foxtel is essentially occupying 3/4 of a satellite’s capacity.
The total data rate of all channels combined is 1.05Gbit/s. That’s a HECK of a lot of data to push. Calculating based on 7Mhz DVB-T channels, coded at 64QAM with the same modulation as our current freeview services, this equates to about 46 physical 7Mhz channels worth of data.
A determination of the services carried and their names can be made based on the metadata. Unfortunately, further information about the codec used is unknown – say where the Audio is MPEG-2 (as reported by TSReader), it is likely to be MPEG-1 Layer 2, and where AC3 is reported, it is likely to be 5.1 channels.
There are some variances on the measured audio bitrate as it seems to include some overhead. Further to that, there are also some multiple-stream services, and many virtual channels. Where multiple streams are encountered, the service housing the largest number of streams has the bit-rates of each stream summed, and the other services using the streams designated virtual channels. I can’t say this is 100% accurate, because this was processed and analyzed manually.
Almost all services which are HD were carried over the DVB-S2 channels in H.264 mode with AC3 audio. H.264 offers better coding efficiency which allows it to give the same picture quality in half as many bits as MPEG-2. It is part of the DVB-S2 standard, so once all receivers are upgraded to the standard, Foxtel can get the advantage of higher modulation modes giving more bit-rate, and each channel using better encoding which requires less-bit rate per channel.
Many services saw audio bit-rates of 256kbit/s and also the availability of AAC audio at 384kbit/s or thereabouts, with many sports channels gaining video bit-rate over the other channels, while simultaneously seeing a reduction of their audio bit-rates. If we’re a sporting nation, I think it’s most clear when you examine the bit-rates devoted to sport channels …
Based on summing up the service data, we can see the carrier utilization. Some carriers are definitely under-utilized.
The thing to keep in mind is that the portion labelled “Other Data + Unused” may have about 3Mbit/s used in EPG (SDT), CA and NIT data updates, and other carriers may have a high proportion of data-services based data which isn’t accounted for when counting up the video/audio bit-rates. A more reliable way would be to count the bit-rate for the null packet stream, but I didn’t do that so we’ll just sit on this one for now.
Most carriers are well-used though, the total pay-load for the snapshot shows 821.1779Mbit/s being used, with 172.2161Mbit/s either unused, or carrying overhead data. Conservatively, we can say there might be about 100Mbit/s of “free room” on Foxtel Satellite, which could allow for the deployment of about 10 HD services.
First, lets take a look at the Radio service bit-rates.
Because most of the services are coded with MPEG-2 (as reported by TSReader, but almost certainly MPEG-1 Layer 2), the bit-rates used are likely 128kbit/s, 160kbit/s, 192kbit/s, 224kbit/s and 256kbit/s.
The MPEG-2 (presumably SD) channels are the bulk of the Foxtel line-up (of over 265 channels) and their allocation follows an almost “gaussian” like curve. Nice!
We’ll take a closer look at the bit-rates in the next part, but lets also look at the bit-rates for the HD channels (identified with HD in their name):
The red coloured services identify the HD services which are encoded in MPEG-2.
Bitrates compared with Freeview
Here’s the quick low-down on bit-rates:
Well what d’ya know? The bitrate for Foxtel radio services outdoes the Freeview, but the Freeview bit-rates are better for other services. But that, in itself, isn’t the right conclusion. Considering that Foxtel used H.264 for most HD services, they need half the bits to bring the same quality – so it’s a victory for Foxtel on Radio and HD. As for the SD, the difference is so small that errors and differences in encoder implementation could make up for it, so it’s a tie when it comes to SD.
I guess I’m rather disappointed to find that Foxtel doesn’t have a big leg-up over Freeview in all cases, given the pay-nature of the service, but satellite bandwidth has always been one of the most expensive transits available, and lowering quality to save costs on that has always been the aim of most satellite operators. By satellite standards, Foxtel is doing pretty good!
That being said, as Foxtel is a paid network, if they choose to upgrade everyone’s receivers (a fairly big cost), they could improve their satellite usage (more data per bandwidth, so can reduce carriers, increase quality, or increase number of services).
Uh, don’t let the NSA lead you into believing that metadata isn’t important? Haha. Jokes aside, it’s been interesting to see all the services I can’t watch, and all the bandwidth that isn’t useful to me. It’s been a good lesson into how quality has to take a back-seat where the transmission medium (and standards, decoder boxes etc) is the limiting factor. Freeview isn’t so bad after all … not compared to some other (not Foxtel) satellite providers.
I wonder whether Foxtel Cable is done in the same way … DVB-C uses higher order modulations, so the channels do have higher bit-rate capacity – I wonder if that means cable watchers actually get even better quality, or do they just shrink the channel usage instead?
More on the satellites when I get time …