Today marks the official launch of 7flix, Channel 7’s new movie-oriented channel. Since the channel is now running actual content, the configuration of the encoders should have reached their “production ready” state, so lets see where the chips have landed.
The transport stream was recorded over a period of over one hour to derive the following information.
From observations of the services, it seems several changes have been made since the last observation. The main Channel 7 station has reverted to stereo encoding rather than joint-stereo, and TV4ME has reverted to a slightly higher horizontal resolution of 528x576i after being at 480x576i for a short while. This could be because some TVs displayed the wrong aspect ratio for the 480x576i stream or because the quality was not sufficient. As I had predicted, 7flix retains the same encoding type as in the loop-days, but now has a closed-captioning text PID to allow for subtitling to be broadcast, and also has a HBBTV private stream for Smart TV usage.
In terms of the bitrate evolution, it seems that 7Digital has edged up a hair, but 7TWO and 7MATE have both lost bitrate to prop up 7flix. As I had predicted, there was no way for 7flix to run decent video on as low as 800kbit/s, so now it’s actually running at about 3Mbit/s which is quite a high bitrate for an H.264 encoded SD service. The remaining bitrate contribution is made up by reducing the crazy 1.2Mbit/s of null packets to just under half of this, also as I had predicted. However, watching it on my TV still shows signs of posterization and overly smooth areas, which may be a result of using live encoders which are not as efficient as offline encoders. Both TV4ME and RACING.COM retains the same bitrate.
This is borne out by looking at the raw PID-rates table.
It seems that stat-muxing is here to stay and is operating aggressively. Even on a short sample recording of the transport stream, it can be seen that bit-rate trading between the main 7 Digital, 7mate and 7flix is occurring, with the other services less affected or already at their fixed limits. As a result, the bitrate analysis is only exact for the period I surveyed the channel, and could vary significantly depending on the programming on the channel. That being said, as my rates are averaged over greater than one hour, it is more representative than an instantaneous spot reading.
If you have trouble …
The results of today’s check on Channel 7’s multiplex will not please all viewers, partly because DVB-T did not standardize on MPEG-4 family of codecs, at least not when many of the older set-top boxes and TVs with integrated tuners were built.
If you still receive the other Channel 7 stations properly, but are having trouble with 7flix, TV4ME and RACING.COM, then you are likely to own an older unit which does not have any support for either MPEG-4 H.264 AVC video or MPEG-4 HE-AACv2 audio.
Your symptoms may include:
- Black screen with no video or audio indicating your tuner supports neither MPEG-4 audio nor video.
- Vision with no audio indicating your tuner supports MPEG-4 H.264 video but not MPEG-4 HE-AACv2 audio.
- Vision with noise as audio indicating your tuner supports MPEG-4 H.264 video but did not identify the audio stream correctly and is decoding it incorrectly, or cannot actually decode MPEG-4 HE-AACv2 audio.
As it seems that they have settled on using these MPEG-4 modes as a necessary evil to ensure their bit-rate budgets and quality of service targets are met, your choices are limited.
- Check if there are any firmware updates for your particular device, and apply them to see if there is any improvement. Note that if you do this incorrectly, you could permanently brick your device.
- Purchase a new tuner or TV with MPEG-4 H.264 AVC video and HE-AACv2 audio support, however, this could get expensive and result in you losing out on TV-integrated PVR functions.
- Use a PC-based TV tuner which returns raw Transport Stream data and uses software codecs to decode the stream – my over 10-year old tuner is running these analyses, so yes, it will still work into the future if they choose to use even newer codecs (e.g. H.265/HEVC) on the air.
- Remove the channels from your program list or ignore their existence while silently fuming inside. Maybe try telling someone, not that it’s likely that will change anything.
Unfortunately, there seems to be no way to tell in advance whether a particular unit supports HE-AACv2 audio from the outside as it doesn’t seem to be part of the Freeview certification process. It seems like buyers are in a “buy and try” conundrum with this one.
There’s never any free lunch, and with a limited bit-rate budget, instead of launching an HD simulcast station, Channel 7 has decided to launch a movie-oriented channel using purely MPEG-4 codecs while retaining their high definition MPEG-2 based 7mate. This is unique in the Freeview DVB-T system so far where most other broadcasters have not employed any MPEG-4 audio codecs, staying with MPEG-1 and AC3 (which are mandated codecs for Australian DVB-T) likely because of compatibility issues.
Unfortunately, this means that bitrate pressures are high which has resulted in the effective deployment of stat-muxing to counteract this to some extent, but also means that bit-rates overall may have suffered. MPEG-4 was a necessary evil to ensure quality of service of their main channels are affected as little as possible.
Sadly, some people using older/cheaper devices without the MPEG-4 decode ability are seeing nothing, or video with no audio or noise, and will end up missing out on it unless they upgrade to newer devices.