[mythtv] (Request) Possible to retransmit not-unpacked MPEG from an ATSC device out over IP?

[Karl Dietz]

On 26.02.2013 03:29, Benjamin Vander Jagt wrote:
> Hi, apologies in advance if I'm in the wrong place.
>
> I work at a WISP in northern Virginia, USA. We are trying to find a way
> to pull in local TV stations, which due to our terrain are hard to get
> without a tall antenna pole. We have antennas on top of towers on top of
> mountains. Our original plan was to build a MythTV box at each antenna
> site, load it up with simple ATSC tuners, such as ATI TV Wonder 600
> USB's, re-compress them on the fly using x264/ogg, and multicast them to
> our wireless customers as a complimentary service.

Pulling in ATSC and recompressing to H.264/AAC sounds like a job that
can be done well by MuMuDVB. (don't let the DVB in its name trick you,
it appears to also do ATSC :)
I'm lurking on their list and they appear to have lots of experience
around turning TV broadcasts into IPTV streams.

> We already checked into the laws, and we've got that sorted out. We can
> get the equipment, and re-streaming x264 is no big problem for our
> servers. It's all our network, so bandwidth isn't a huge problem, though
> we would like to try to keep the channels low-bitrate for now, since
> some of our customers are almost 80 miles away and therefore are limited
> to around 1 megabit. The problem is, as you know, transcoding hurts
> quality.

Transcoding will hurt quality, but without transcoding there is no way
to fit a 8 mbit/s stream in a 1 mbit/s pipe :)
I'd try something around 4mbit/s for HD+one 5.1 audio first, starting
with less is likely not enjoyable. Then try 2mbit/s for 1/4HD+Stereo and
at your 1mbit/s target run 1/16HD+stereo. (using the MPEG-2 HD video
stream as source for the smaller streams may improve quality per bit
over using the SD material as source)

> It seems to me that there ought to be a way to use the ATSC tuners to
> pull in the compressed stream from the air, let MythTV backend send it
> out to clients in UDP, and let the client ends decompress the streams
> however they want. Am I missing some technical detail that makes this
> all not possible?

MythTV isn't the right hammer for this nail. But it will happily record
the streams produced by either MuMuDVB or a comparable hardware
solution.

Keep in mind that wireless point-to-multipoint transmissions may have
some special stuff wrt multicast. e.g. in WiFi the transmission rate is
reduced for multicast packets, maybe there is something similar in your
backbone. But your network people should know if you can push multiple
multicasts down the point-to-point backbone links without special
tricks.

Regards,
Karl