Re: [RE] Rev1 of my 1st presention at May meeting is in ResE area
Geoff wrote:
> I assume that the 19.4 Mbit/s rate is for 1080i29.97
> or 1080p29.97, and the 38.4 Mbit/s rate is for 1080p59.94.
That's not the case.
The ATSC spec simply notes that terrestrial technology can
carry "about 19 Mbps" of data per 6Mhz channel, and cable
can carry "about 38 Mbps" of data per 6Mhz channel. ATSC
is really a "data broadcasting" standard.
Separate from the data pipe capacity discussion, the ATSC
spec (and other ATSC specs) define how specific types of data
should be constructed/encoded, including audio and video.
For video, the ATSC spec specifies 36 (was 18) valid video
compression formats which only go up to 1080p30. There are no
1080p59.94 or 1080p60 formats! Further, the format table does
not list bitrates!
For audio, there are also format specs.
All said and done though, the broadcasters choice of video bitrate,
audio bitrate, PSIP (basic EPG) bitrate and other bitrates, when
aggregated into a MPEG-2 Transport Stream, must fit into the "about
19 Mbps" terrestrial datapipe or the "about 38 Mbps" cable datapipe.
A broadcaster could choose to encode SD video at 19Mbps (overkill),
or choose to encode HD video at 5Mbps (will look really bad).
Again though, 1080p30 is the current ATSC limit, and there is no hard
link (requirements) between video formats and bitrates.
While the ATSC spec suggests that cable could carry video up to
38.8Mbps,
I don't know if the CableLabs and SCTE specs (and Cable MSOs) support
that.
Thomas Gilg