hi thanks for your answers
my symbol rate is 300 ksps
using this calculator
http://www.satbroadcasts.com/DVB-S_Bitrate_and_Bandwidth_Calculator.html
and these settings : QPSK rate 1/2 FEC frame 64800
i get 276.5 kbps of TS bitrate
here are my settings for ffmpeg :
*ffmpeg -re -f lavfi -i testsrc=s=640x480:r=25:n=1 -vf
"drawtext=text=%{localtime}:x=(w-tw)/2:y=h-th-37:fontsize=20:fontcolor=yellow:borderw=2:bordercolor=black"
-pix_fmt yuv420p -an -g 25 -b:v 228k -c:v libx264 -tune zerolatency
-maxrate 228k -bufsize 230k -nal-hrd cbr -f mpegts
udp://127.0.0.1:1234?pkt_size=188 <http://127.0.0.1:1234?pkt_size=188>*
this generates a test pattern very close to 275 kbps
as i'm very close to the DVB-S net bitrate i get a near constant output
power (with some small gaps) and SDRAngel is quite happy
i will play with the -muxrate option to see if this keeps tightly the
bitrate at maximum limit
best regards
Bob
Le ven. 8 févr. 2019 à 13:22, Raydel Abreu (CM2ESP) <[email protected]> a
écrit :
> Hi Ron
>
> That formula it's very useful! Thanks. I have a silly question (sorry for
> it). If I understand correctly 8000000 is the symbol rate and 12901961 is
> the TS rate? Correct?
>
> The multiply by 2 is because Tx signal is QPSK? If that's so then it will
> be 1 for BPSK, 3 for 8PSK and so on.... Am I right?
>
> Thanks!
>
> Raydel
>
>
>
>
> El jue., 7 de feb. de 2019 7:26 PM, Ron Economos <[email protected]>
> escribió:
>
>> First, you have to match the TS rate to the symbol rate. The equation is:
>>
>> Symbol rate * 2 * 188/204 * code rate
>>
>> For the example flow graph:
>>
>> 8000000 * 2 * 188/204 * 7/8 = 12.901961 Mbps
>>
>> Second, you need to constrain the video bitrate to fit into the selected
>> TS bitrate. With ffmpeg, something like this:
>>
>> ffmpeg -i test.mp4 -c:v libx264 -b:v 10M -minrate 11M -maxrate 11M
>> -bufsize 8M -c:a copy -muxrate 12901961 test.ts
>>
>> For SD video, a smaller bufsize like 2M should be used.
>>
>> Ron
>> On 2/7/19 15:15, Alban Meffre wrote:
>>
>> Hi All
>> did some transmission test in DVB-S tonight
>> TX : ffmpeg + gnuradio + pluto SDR
>> RX : RTLSDR + sdrangel
>> it works but there are some gaps in the received signal because the TS
>> stream bitrate is slightly less to the maximum usable bitrate
>>
>> is it possible to add some bit stuffing at DVB-S modulator side to make
>> to output power constant ?
>>
>> Bob
>>
>> --
>> Alban MEFFRE F4GSW
>>
>>
>>
>> _______________________________________________
>> Discuss-gnuradio mailing
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>>
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>>
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--
Alban MEFFRE F4GSW
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