Re: playback of live HDV stream

On Thu, Jan 29, 2009 at 1:51 PM, Tom Mercelis <[email protected]> wrote:
> Hi,
>
> I want to stream the video (and audio) from 3 HDV camera's to 1 (or
> possibly several pc's). Today I tried a very simple "proof of concept",
> using
> dvgrab -f hdv - | nc -u 10.8.2.240 4090

Technically, the correct way to do this is to encode a discrete number
of transport stream packets, each 188 bytes, into a single udp packet
based on the MTU. For an ethernet MTU of 1500, that gives 7 TSPs per
UDP packet. I have some simple, very short python code that does this
if you don't want to use nc.

> and
> then opening "vlc udp://@:4090"
> or "nc -l -u -p 4090  | mplayer -"
>
> This works, but the delay is around 3 to 5 seconds.
> The primary goal of these live images would be so a "director" can
> direct (with an intercom system) the camera operators. Obviously a lower
> delay would be preferred.
>
> Are there any buffers in dvgrab (when used with mpeg 2 TS from HDV) that
> might cause a significant delay (and aren't strictly necessary)?
> I see the -buffers option wich defaults to 100 "frames", these frames,
> are it video frames, or firewire packets, or something else?

Yes, there are a fair amount of buffers in dvgrab because it is
primarily for disk recording. Also, it does some buffering in the
course of parsing to extract time and date metadata. You can reduce
these from the default of 100 using the -buffers options.

I suggest you take a look at the test-mpeg2 example program from the
libiec61883 package. This is the same library dvgrab uses. However,
this example does not do any buffering. By default, it receives to
stdout, ready to piped. It might be all that you need.

-- 
+-DRD-+

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