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F_Null Packet vs. Null Packet

Postby mucsb » Sun 21 Feb 2021 16:08

Dear All,

recently I started to detect F_Null Packets in my own transmission. The picture does not build up. Does someone know what is this kind of packet for? See attached.


I am familiar with the regular Null Packet but this is somewhat different.
Attachments
F_Null packets.png
F_Null packets.png (25.94 KiB) Viewed 145 times
mucsb
 
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Re: F_Null Packet vs. Null Packet

Postby F6DZP » Sun 21 Feb 2021 22:02

Hello,

when you set the SR and Fec and modulation there is a TS bitrate that correspond.

If your video data + audio data + DVB tables are lower than this bitrate, the multiplexer is supposed to add null packets to give the TS bitrate needed.
If, for some reason, your multiplexer doesn't give the good TS bitrate but a lower bitrate, then, if you are using the F5OEO Pluto firmware, it adds itself Fake Null Packet to be sure that your modulator will have the good TS bitrate.

Normally you should have only Null Packets. I have added the detection of Fake Null packets in Minitioune to let people know what is happening to their final TS data.
If you have only Fake null Packets that shows that you have 2 problems :
1) no Null packets => you give too much bitrate to video + audio data so no place for Null packets. That will produce some problem with encoding datarate variations that always exist even you are in CBR mode
2) there are Fake null Packets => that indicate that you have set the TS datarate of the multiplexer too low, so it is the Pluto firmware that must add Fake Null packets to be sure that the final TS bitrate will be good.

Jean-Pierre F6DZP
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