Alban,
It's absolutely critical that you use the -muxrate option in
ffmpeg. If you don't, you get a variable rate Transport Stream, which is
guaranteed to cause problems.
Also, I would specify the muxrate to 1 bps of accuracy. ffmpeg supports
it. So for 300 kSyms/s, it would be 276471.
You don't really need the -nal-hrd cbr parameter. The video bitrate can
be variable, but the peak video bitrate (combined with the audio
bitrate) can't exceed the TS rate.
BTW, the RF power output is not changing. It's just the player not being
able to decode the bitstream properly.
Ron
On 2/8/19 09:59, Alban Meffre wrote:
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]
<mailto:[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]
<mailto:[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
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--
Alban MEFFRE F4GSW
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