hi thanks for your answers
my symbol rate is 300 ksps
using this calculator
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
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) <cm2esp@gmail.com> a écrit :
_______________________________________________Hi RonThat 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!RaydelEl jue., 7 de feb. de 2019 7:26 PM, Ron Economos <w6rz@comcast.net> 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 Alldid some transmission test in DVB-S tonight
TX : ffmpeg + gnuradio + pluto SDRRX : 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
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Alban MEFFRE F4GSW
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