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What's On, Transponder and channel support
Transponders & channels
Which are the satellites used for cable and freeview feeds?
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<blockquote data-quote="Fisty McB" data-source="post: 1081918" data-attributes="member: 389824"><p>The Astra analogue service (which closed by the end of 2001) was effectively an infill for those outside of its terrestrial service area, and in any case would not have been a useful backup to the main satellite distribution as it is quite likely that were the main feed to fail due to external interference, then it's unlikely a feed from Astra 1D would have been useful either. Without knowing how they were arranged, it would appear to me that splitting the TX feeds over two different satellite positions was to allow a backup to be put in place, so if the feed from 18W failed at a particular site due to receiver failure then 37.5W could kick in and vice versa. </p><p></p><p>As to the suitability of using the intended DTH broadcasts from 28E for DTT use, the big issue here is that the TV channels on satellite will be stat-muxed and will therefore vary over time. To insert them into a DVB-T/T2 multiplex you'd either have to know what is the maximum allowed bitrate of the video stream so you can ensure all video streams can be accommodated on the multiplex without going over capacity, which would mean an awful lot of null bits being required and thus a lot of capacity wasted, or reencoding of the feed into the multiplex which obviously takes a hit on the output picture and audio quality - you want the lossy picture output to be first generation where possible. In the analogue days for cable providers this wasn't an issue, as many of the channels they provided were fed to them via Astra 1 that they could simply decode and insert into their network (some channels were fed via alternative satellite positions, 27.5W was once quite popular) but for DVB-C transmissions they could only take a direct satellite feed either as the entire content of a satellite transponder/multiplex from DVB-S to DVB-C and recode a new Network Information Table in the DVB-C signal, or take a channel whom was operating at a fixed bitrate for video as well as audio, this being predictable to insert into a DVB-C multiplex. Nowadays, most indivudal channels on Virgin Media's network provide the operator with either an uncompressed or lossless feed which VM encode into a multiplex before being sent for distribution.</p></blockquote><p></p>
[QUOTE="Fisty McB, post: 1081918, member: 389824"] The Astra analogue service (which closed by the end of 2001) was effectively an infill for those outside of its terrestrial service area, and in any case would not have been a useful backup to the main satellite distribution as it is quite likely that were the main feed to fail due to external interference, then it's unlikely a feed from Astra 1D would have been useful either. Without knowing how they were arranged, it would appear to me that splitting the TX feeds over two different satellite positions was to allow a backup to be put in place, so if the feed from 18W failed at a particular site due to receiver failure then 37.5W could kick in and vice versa. As to the suitability of using the intended DTH broadcasts from 28E for DTT use, the big issue here is that the TV channels on satellite will be stat-muxed and will therefore vary over time. To insert them into a DVB-T/T2 multiplex you'd either have to know what is the maximum allowed bitrate of the video stream so you can ensure all video streams can be accommodated on the multiplex without going over capacity, which would mean an awful lot of null bits being required and thus a lot of capacity wasted, or reencoding of the feed into the multiplex which obviously takes a hit on the output picture and audio quality - you want the lossy picture output to be first generation where possible. In the analogue days for cable providers this wasn't an issue, as many of the channels they provided were fed to them via Astra 1 that they could simply decode and insert into their network (some channels were fed via alternative satellite positions, 27.5W was once quite popular) but for DVB-C transmissions they could only take a direct satellite feed either as the entire content of a satellite transponder/multiplex from DVB-S to DVB-C and recode a new Network Information Table in the DVB-C signal, or take a channel whom was operating at a fixed bitrate for video as well as audio, this being predictable to insert into a DVB-C multiplex. Nowadays, most indivudal channels on Virgin Media's network provide the operator with either an uncompressed or lossless feed which VM encode into a multiplex before being sent for distribution. [/QUOTE]
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What's On, Transponder and channel support
Transponders & channels
Which are the satellites used for cable and freeview feeds?
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