While I was on holidays, the DVB-T digital TV stations at home were undergoing the last of a series of long-anticipated changes. On 8th April 2017, SBS followed the lead of the other broadcasters and finally converted over to MPEG-4 H.264 for delivery of their high definition services, and added SBS VICELAND in HD. This now completes all five major broadcasters’ transition to H.264 high definition, although MPEG-2 standard definition is still retained for backwards compatibility with set-top boxes and older sets incapable of decoding H.264 encoding.
Of course, such changes make for a good reason to re-examine the multiplex configuration to assess how the bitrates have changed, and what encoding is in use. As a result, soon after returning from overseas, I set to work on analysis.
A Few Stumbles (… grumble, grumble …)
Prior to leaving on holidays, I had powered-down the maze of wires that I call my bedroom and packed away any surplus wires that would not be in use so they would not be damaged by people potentially tripping over them. For increased reliability, I also removed any splitters or amplifiers that wouldn’t be in use – after all, I didn’t want any calls while I was on holiday about things breaking.
When I returned home, it seemed they had gotten used to the cleaner configuration, and I spent the first few days re-energizing everything. The amplifier/splitter and cable that used to get an aerial connection in my room was not restored, since the family seems to have gotten used to not having an extra cable to trip over. As a result, I had to go elsewhere for my connection.
Downstairs, I am still running my TV tuner server with a few extra free ports on the eight-way amplified splitter. As a result, I set up a laptop with a few tuners and decided to do some transport stream capturing.
Unfortunately, as I didn’t realize, I chose my older HP Probook 4525s with an AMD Phenom II P960 CPU in it. Using my two old Twinhan VP-7045 tuners, the captured streams were badly garbled after a few minutes, not because of reception issues, but timing issues it seems. Maybe the AMD USB controllers or the CPU had problems with the driver, but the issues were so bad that they weren’t solely runt TS packets requiring re-synchronization. A whole day was wasted thanks to this.
So I grabbed the Lenovo E431 I took on holidays, moved my holiday data elsewhere, and restarted capturing with that. This time it was successful, although I attempted multiple times to try and get three hours of solid recording without a single TEI or CRC error. I was successful on two of the five multiplexes, with only minor errors on the other three (<100 TEI and CRC errored packets combined). Previously, I would have gotten clean captures if I had tried twice. Seeing as I had already wasted so much time on data acquisition, I wasn’t going to try again – 100 packets is only 18.3kiB of data in about 29GiB, which is insignificant to the analysis anyway.
As a result, I had about 145GiB of data sitting for me to analyze, but due to more pressing commitments to do other work, analyze data from my holidays and process the photos I’ve taken (still ongoing), I didn’t begin analyzing this data until today. As a result, the analysis is late but the data reflects what was on the air about ten days after SBS’ switchover.
The updated service summary table is above with differing results from prior analysis done at the end of 2016 highlighted in red text, and summarized as follows:
- As usual, channel 7’s audio mode changes from time to time, and at the time of analysis, was stereo instead of joint-stereo.
- SBS, as noted, has launched SBS VICELAND HD which is H.264 [email protected] in 1080i with MPEG-1 Layer II Stereo audio at 192kbit/s.
- SBS HD has been renamed to SBS ONE HD and has been converted from MPEG-2 to H.264 [email protected] in 1080i.
- A new audio service named SBS Arabic 24 has been added to their multiplex, carrying MPEG-1 Layer II Stereo at 128kbit/s.
- ABC has changed the audio codec for ABC HD from Dolby AC3 2-ch to MPEG-1 Layer II Stereo at 256kbit/s.
In terms of the high definition services, it seems the commercial broadcasters have settled to use Dolby AC3 audio encoding, whereas SBS and ABC have both decided to use MPEG-1 Layer II Stereo. This decision may well have to do with compatibility – even though Australian DVB-T compliant boxes are required to be able to decode AC3, some imported devices may not be able to do so. By changing over the audio mode, maybe they can address the small slice of devices that support H.264 video, but not AC3 audio (possibly imported USB TV tuners?). The change on ABC has actually liberated a little bitrate, as the MPEG-1 stream is smaller than the AC3 stream they formerly broadcast. At this moment, the only other codec used is MPEG-4 HE-AACv2 on RACING.COM, which probably has quite limited compatibility but minimizes bitrate requirement.
When it comes to multiplex utilization, it seems that Seven is doing a bad job again. There’s almost enough bitrate to drive another shopping channel in, which was noted previously as a “misconfiguration” but has seemingly recurred. The other carriers are doing better – SBS and ABC seem to have a fairly healthy margin, whereas Nine and Ten are doing their damned best to squeeze out every last bit. Their encoders must be very aggressive to ensure they can keep such high utilization and not end up with a bitrate budget deficit. All broadcasters seem to be utilizing statistical multiplexing, which is expected.
I decided to make a total service bitrate graph with video services sorted with descending total bitrate. As all radio services have settled on 128kbit/s, there was no point including them on the graph. MPEG-4 H.264 video is labelled light green to distinguish from MPEG-2 services in light blue.
In the realm of HD services, TEN HD takes the crown for highest service bitrate, with a significant margin above SBS Viceland HD. This is followed by 7HD Sydney, SBS ONE HD at around the same level, before another small gap, followed by 9HD Sydney and ABC HD. When looking at the bitrates, it seems clear that broadcasters are delivering an H.264 HD service in much the same bitrate as SD services, especially when compared to the past. Even today, it can be seen that SD services can be seen fairly high up the ladder, including Channel 9 Sydney and ABC News 24, remembering that MPEG-2 is less compression-efficient and people are continuing to own larger-TVs which would make low image quality more apparent.
That being said, the bitrate allocation strategies of different broadcasters seem to diverge somewhat:
- Seven appears to have bet the house on HD, and thus their SD “compatibility” service is fairly low down the ladder.
- Seven seems to have bumped up RACING.COM’s bitrate allocation over time – now it has about the same video bitrate as 7 Sydney (SD), but is using H.264 encoding for a better picture. To continue broadcasting at “reduced resolution” 640x576i seems a little unnecessary in light of this. It continues to retain a high-efficiency audio stream.
- Seven seems to prioritise its secondary services in reference of 7mate Sydney, with 7TWO Sydney sitting fairly average and 7flix so severely neglected that it sits “next” to the shopping channels. Of course, if their multiplex utilization was better, they could have this changed in a jiffy.
- Nine seems to have done the opposite, allocating its SD service a generous amount of bitrate, while having the HD service deal with slightly less.
- Nine relegates the shopping channel Extra to the bottom of the ladder – where it arguably belongs, to make the most bitrate for its auxiliary services.
- Nine’s secondary services of 9Go!, 9Life and 9Gem share roughly similar amounts of bitrate.
- Ten has also bet the house on HD, with the compatibility SD service about middle-of-the-pack similar to the bitrates of Nine’s secondary services.
- Ten appears to prioritise ELEVEN over One with a noticeable gap in allocated bitrate. As expected, their shopping channel SpreeTV sits second-lowest on the ladder, as expected.
- Ten’s other shopping channel, TVSN, has a noticeable bump over SpreeTV for some reason (maybe money?), and occupies about the same bitrate as the most neglected secondary services of other broadcasters.
- SBS has very much embraced HD with SBS VICELAND HD occupying the largest slice of their bitrate, followed by SBS ONE HD.
- Unfortunately, as a result, the SD compatibility broadcasts of SBS VICELAND and SBS ONE sit quite low, close to TVSN (a shopping channel).
- SBS prioritises the Food Network secondary service, which sits a little higher up the ladder (but still below average), while NITV occupies the low-bitrate corner with the above services.
- ABC’s SD service and HD service seem to occupy similar levels of bitrate, along with their secondary ABC2/KIDS service. Some equity, it seems.
- Instead, ABC seems to given ABC News 24 a significant boost – probably to compensate from going from HD to SD on MPEG-2 and having sharp text to read, where image quality issues might be more obvious.
- ABC seems to have de-prioritised ABC ME in comparison to their main services.
Finally, in case you are interested, here are the recorded ‘per-PID’ rates. Note that the totals vary slightly due to the bitrate determination method which requires knowing the file duration as precisely as possible. It’s not 100% accurate, but it should result in bitrates no more than 2kbit/s in error for the whole multiplex and <0.05kbit/s per PID.
Bitrate Evolution over Time
Since readers seemed to have liked it so much the last time I did this, I decided to create updated bitrate evolution graphs.
Both 7 Sydney and 7TWO Sydney have maintained much the same bitrate as the last analysis. However, 7HD Sydney saw a large fall in bitrate, and 7flix saw a minor fall. The only service that reversed this trend was RACING.COM which has been creeping up slowly. However, the difference in bitrate has been mostly lost to poor multiplex utilization, with lots of null packets being emitted.
Channel Nine is a picture of stability. Nothing ever seems to move much at all. Makes things simple?
A similar thing can be said of Channel Ten as well – mostly maintained the same readings plus or minus a small amount.
ABC seem to have done a little tweaking. ABC News 24 was the major winner being given a bump up in rates, whereas ABC1 seems to have been slowly shaved somewhat. ABC2/KIDS has gotten a shave, whereas ABC ME held stable and ABC HD gained slightly.
It seems that every SD service was given a slight reduction in bitrate, with SBS HD being cut “in half” while being upgraded to H.264 to make way for SBS VICELAND HD.
Owing to a number of commitments and hurdles to overcome, the analysis of Freeview for when SBS changed over to H.264 had been delayed. At last, it is delivered, almost two months after the fact, analyzing data from 18th April 2017.
The results are not unexpected, but signal a uniform move in HD services to using MPEG-4 H.264 [email protected] encoding at 1080i. However, there is a mix when it comes to audio, with commercial broadcasters preferring Dolby AC3, and ABC/SBS preferring MPEG-1 Layer II Stereo.
Bitrates are beginning to be more homogenous, with HD services occupying a similar bitrate to SD services, but the allocation strategy differs with the broadcaster. Overall, it does seem that some SD service bitrates have fallen over time and RACING.COM has increased over time which is slightly disappointing. It seems that viewers with incompatible equipment that are forced to view SD “compatibility” services may be receiving reduced picture quality with some broadcasters which prefer to allocate more bitrate to enhance the HD service over providing a quality SD experience. This is probably fair, as SD equipment is getting a bit rarer over time and people upgrade their reception equipment.