Yesterday marked the launch of ABC HD, which finally means that Sydney Freeview gets each broadcasters’ main stations in high definition at long last. (EDIT: Actually, not quite true, as 7HD Sydney is still a simulcast of 7mate.) According to the launch material, the broadcast would be made in MPEG-4, but of course naturally people did ask me to analyze the service.
Around this time last year was when I last did a comprehensive check of Freeview transmissions, and since then, much has happened which has been captured (at least partially) through interim postings such as these. It gets a little messy to comb through them all, so instead of issuing an interim Freeview Update, I’ve decided to redo the analysis entirely to take another yearly snapshot.
As a result, I am awake at 4am … writing this post. No kidding.
As most, if not all stations have moved to statistical multiplexing, spot bitrates can vary wildly. As a result, I take a transport stream recording of the whole multiplex for a period of 3 hours (+/- 1 minute) to average out the bitrates with. The recorded TS files are checked for time, and the bitrates are determined by dividing the size of the demultiplexed PID streams versus the record time. Due to slight inaccuracies in determining record times, total multiplex bitrate is likely to vary by a few kbit/s, but each PID stream bitrate should still be accurate to at least the kbit/s level. The streams were analyzed using TSReader.
The service summary table is shown above. As I haven’t kept my eye on Freeview for a while, a few changes have happened:
- RACING.COM channel’s audio bitrate has gone down from 64kbit/s to 48kbit/s.
- SBS has stopped using 704x576i and 1440x1080i formats and has reverted to the full-size frame formats. Joint-stereo audio has reverted to full stereo coding, and SBS TWO has been renamed to SBS VICELAND. A private stream has been allocated to Food Network where formerly it was sharing with another channel.
- TEN HD has moved up to High@L4 profile from previously using Main@L4, which should bring more compression efficiency.
- ABC’s launch of ABC HD using MPEG-4 H.264 High@L4 with a frame size of 1920x1080i, along with Dolby AC3 2-ch audio at 384kbit/s. The News24 service reverts to standard definition with MPEG-2 video and MPEG-1 audio.
- These changes mean that all HD services are now 1920x1080i at 25fps. No more 50fps services are on the air. Furthermore, all channels except SBS HD have standardized on High@L4 profile.
In regards to channel video bitrate, here is the ranking, sorted by bitrate from high to low:
The three shopping channels (in purple) that still are on the air still consume around 1.7-2.3Mbit/s video bitrate. Unfortunately, when it comes to services you’d like to watch, their bitrates are starting to look less healthy.
SBS HD (in red) is the outright leader on absolute bitrate, but this is because it is still using the older MPEG-2 encoding. This allows for older HD sets to still receive HD, but the price is about half the bitrate efficiency of MPEG-4. Even then, it should compete fairly well with the majority of MPEG-4 HD stations based on the fact its bitrate is almost double.
MPEG-4 services (in green) vary somewhat with respect to bitrate. 7HD and TEN HD both have more generous bitrate allocations, especially compared to 9HD. ABC HD has barely the same bitrate allocation as many standard definition channels. This may change in the future, as at this point, the launch of ABC HD is relatively underwhelming with all the content I’ve seen being merely upscaled SD content.
Looking at individual broadcasters, it seems that Channel 7’s push towards HD leaves its standard definition version relatively strangled with just 2.8Mbit/s of bitrate, and 7 TWO isn’t looking that well with 2.5Mbit/s which is only the same as RACING.COM also carried by Channel 7 but in MPEG-4. The 7flix service fares slightly better with 2.9Mbit/s. The only Channel 7 SD service that has a decent bitrate is 7mate raking in 3.7Mbit/s.
In the case of Ten, the services show more healthy bitrates overall. Channel 9 seems to continue to prioritise and balance the SD service with the HD service a lot better, so that SD viewers aren’t seeing a poor picture, although their secondary services have less bitrate.
In fact, it seems that SBS is the one that is really feeling the pinch, due to their all MPEG-2 services, their channels are towards the lower end of the bitrate spectrum. Food Network is their highest bitrate channel outside of their HD service, and VICELAND is even below RACING.COM and only just slightly ahead of the best shopping channel. This is somewhat disappointing to see.
ABC seems to continue broadcasting a good primary SD service, and their ABC2/KIDS is the highest bitrate SD service at the time of survey. Their other services (ME and News 24) both rank fairly well. It seems their HD service has a more “SD-like” bitrate for this balance to occur.
Overall, it seems that standard definition viewers are feeling the bitrate pinch. Where previously the primary standard definition channels may have carried 4-5Mbit/s of bitrate, the increasing pressure of new channels, the need for MPEG-2 simulcasting and the carriage of “non-essential” channels has resulted in the average SD service video bitrate getting closer to 3Mbit/s.
A closer look at the ABC multiplex bitrate evolution shows that for the most part, the ABC2/KIDS service has seen a slow increase in rates, the ABC3/ABC ME service a slow decrease in rates, and the main SD channel has been holding fairly stable although trending towards a slight reduction. News 24 took a major cut and went back to SD to allow for the launch of ABC HD.
Looking at the per-PID rates, it seems that ABC HD may indeed pick up more bitrate in the order of up to 1Mbit/s as the multiplex has a lot of nulls compared with most other broadcasters. On the whole, mux utilization for all broadcasters was aggressive with the exception of ABC (1.3Mbit/s free) and Seven (0.6Mbit/s free, twice as much as the others). Due to an improvement in determining the recording time, the reported mux bitrates are now much closer – slight variations are likely due to packet loss due to transient reception errors.
The launch of new HD services is a double-edged sword. On the one hand, for those with more modern sets or computer tuners, we are able to enjoy full HD at long last, using the more modern H.264 AVC MPEG-4 codec. However, the need to keep compatibility with legacy receivers capable of only MPEG-2 video and MPEG-1 audio really means that we are still losing some bitrate there. In some cases where the former HD station was not a simulcast, this also meant “splitting” the bitrate from a former MPEG-2 HD service into an MPEG-2 SD service and an MPEG-4 HD service, resulting in more bitrate constraints on both services.
As a result of the aggressive move by all broadcasters (except SBS) to embrace the MPEG-4 encoding, the HD services are able to look acceptable despite using only marginally more bitrate than a regular SD service. The bias towards the HD service is apparent for 7HD and TEN HD, whereas Nine and ABC are both prioritising their SD services instead.
The failure of SBS to transition to MPEG-4 at this time has resulted in their other SD MPEG-2 services being bitrate starved compared to the competition, and overall, bitrates across the board for standard definition services predominantly lie in the 3Mbit/s region where several years back they would have been closer to 4-5Mbit/s. This is not of great relevance where users are watching the HD primary service, however, will affect all users of secondary services carried by the broadcaster. The number of shopping channels is less than in prior analyses, but their existence only exacerbates the bitrate-limited nature of DVB-T broadcast.
The launch of ABC HD itself is a good thing, but at this stage as many viewers have noted, is rather underwhelming due to the broadcast of only upscaled SD content at most times. The service does have about 1Mbit/s of wriggle room, so it could turn out to be quite competitive with the commercial broadcasters’ HD channels, but at the time it was surveyed, this was not the case.
Lets hope SBS transitions to MPEG-4 on its HD channel to relieve the bitrate starvation on its SD services – after all, it is already simulcasting HD and SD in MPEG-2, so it’s really only gains.
This is a dreary-eyed Gough, signing off for the day …
Update: Service Bitrate Evolution over Time
At the request of one my regular readers who wanted to see more service bitrate evolution graphs for the other multiplexes, I went on a rampage to gather all of my data to allow it to be plotted. Of note is the fact that I don’t do “global” surveys of bitrates very often and depending on the situation (impending channel launch), will only survey one mux at a time. As a result, the number of samples for each multiplex varies, as do their spacing in time.
Due to the number of changes in Channel 7’s line-up, I have a lot of data samples for them. The graph shows just how rocky the history of bitrates for the channels has been, at least on Channel 7’s mux. The main station has swung wildly, but overall the trend is downward as of late, as is with 7TWO. At one point, their bitrates were lower than necessary as the null packet fraction was quite high due to a potential misconfiguration after turning off a channel. TV4ME has left the air, and RACING.COM has increased its bitrate marginally. It seems 7flix has also gained in its bitrate, and 7mate as well, whereas 7HD has lost out over time. The big drop in 7mate corresponds to the launch of 7HD. The days of SD services having 4-5Mbit/s seem to be well and truly behind us.
I don’t have much data for SBS, and that is primarily because not much has happened bar for the launch of the Food Network channel. SBS TWO used to command a fair chunk of bitrate, at the expense of SBS HD which did some mode changes from time to time, but has otherwise been restored to its 2013-level of bitrate. The increase in available bits to accommodate the food network was primarily due to a change at the time of launch to their modulation mode to increase available bitrate as their competing channels. All stations now run 1/16th guard interval, with 3/4 code-rate.
Channel Nine’s strategy seems to be relatively conservative. EXTRA 2 got the axe, freeing up 2Mbit/s. Along with the reversion of GEM to SD, this gave the necessary bitrate to support 9Life and 9HD. All services have been very consistent in bitrate allocation at the sample points.
Ten’s bitrate strategy seems to be a little hill-and-dale. The shopping channel Spree has only drifted downwards marginally, whereas TVSN has sort of gone upwards and levelled out. Ten HD’s bitrate has been relatively stable after the 1Mbit/s “teaser” stage. ONE however, has seen bitrate cuts throughout its high definition life to feed the bitrate increases to TVSN and ELEVEN. However, on the launch of the HD service, the boost to ELEVEN had been cut back noticeably, and the main standard definition channel received its first bitrate cut. This results in all the non-shopping standard definition channels sitting at roughly the same bitrate of 3-ish Mbit/s.
I covered it earlier, but since I found one more data-point, I’ve decided to produce an updated graph. It seems that bitrate movement at the ABC is gradual. The main SD channel has only received a marginal cut to bitrates, with News24 making a big drop as it reverted from HD to SD. ABC2/KIDS had undergone a fairly consistent ramp-up in bitrates, whereas ABC3/ABC ME has trended downwards over time.
I decided to include this particular graph of the now-defunct TVS just for a laugh. Not given the pressures of bitrate budgeting between competing services, its bitrate has been rock-solid right up until it went off the air.