[linux-dvb] Re: Determining transport stream bitrate.

[Jens Thomsen <MisfitsPlan9@access-4-free.com>]

Aurelian Pop wrote:

>  
> > This is probably an off topic question, sorry I don't know who else to ask.
> > Does anyone know how to determine the bitrate of a specific PID in a 
> > Transport Stream. I have some transport streams that I recorded to disk 
> > and now I want to determine the bitrate of the individual PIDs. I know 
> > the total bitrate of the stream, and how many bits have occured thus far 
> > in both the stream and the PID that I need the bitrate for.  I tried this:
> >
> > bits of PID/(total bits in stream/stream bitrate)
> >
> > and It doesn't seem to work.
> >
> >
> > Thanks in advance,
> >    Jens Thomsen
> >
> >    
>
> The simples way is to count the number of packets having the desired PID, then
> multiply this number with 188*8. The result represents the number of bits you
> have in the stream defined by your PID. Then just divide that number with the
> duration in seconds of your transport stream. That's it.
>
> Another way is to look for the PCR values in the adaptation fields and do the
> same calculation taking as reference the PCR. This is more precise, but maybe a
> little bit more complicated.
>
>
> Aurelian
>
>
>
>
>  
I guess I should have been a little more clear.  I would like to know 
the bitrate of certain PIDs
as I see them in the TS.  The idea is that I could hook this program up 
to a live broadcast feed
and collect bitrate statistics real time.  Collecting real time stats is 
probably easier to do,
because then all I have to do is this:

t1 = get current time (ns)
read packet(s)
t2 = get current time
numbits = (number of packets read * 188) * 8
bitrate = numbits/t2-t1

However in a prerecorded stream I don't have that luxury. As I indicated 
in my last message
This sohuld work:

	bits of PID/(total bits in stream/stream bitrate)

because (correct me if I'm wrong):

	(total bits in stream/stream bitrate) = number of seconds in TS thus far

So I want to figure out one algorithm that will work on live **and** prerecorded
Transport Streams.


Jens





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