DATVexpress video settings
Posted: Mon Aug 08, 2016 3:56 pm
I have been experimenting with the video settings available in DATVexpress and made the following notes:
DATVexpress is using FFMPEG libraries for video encoding and so are reliant on that for video Q performance - a couple of FFMPEG parameters are available as UI controls in the Windows software under video codec. These are the Group of pictures or GOP length (known as the N parameter) and the number of B frames between I and P frames or length between two consecutive P Frames (known as the M parameter) and adjusting these can have a significant effect on picture quality. Google has wealth of info including https://ffmpeg.org/doxygen/2.8/structAV ... 5bb9e2d4d4
The other adjustment which has significant effect is the video bitrate twiddle factor - this allows fine tuning of the encoder buffer and is dependent on video bit rate and content. I have found that this should be adjusted on each symbol rate to give an indication of around 1 - 5% on the Tx queue bar graph - no indication means the buffer is under running and the TS will be stuffed with null packets. Higher than 5% and the buffer seems to eventually fill up and will crash the rxr. As you make changes, you can see the video bit rate display change.
The other parameter is Performance which I don't fully understand but only affects H264 and should be set to suit your PC - my i5 machine seems happy with "very fast" but a slower machine should apparently be set to "ultrafast"?!
I find the following parameters give reasonable performance but I am sure there is more tweaking to be done by someone who understand FFMPEG - my RPI encoder and camera still gives better pictures, albeit at reduced resolution, at 333Ks. Setup was i5 laptop with USB composite capture card and Vmix - received using Tutuione.
MPEG-2 1.5 to 4+ Msymbols/sec - GOP = 15 and B frames (M) = 5
H264 below 1.5 Msymbols/sec - GOP = 20 and M = 3
Adjust twiddle factor to 2% - seems to be values around .9
Hope this helps - no doubt more to follow...
73 Noel - G8GTZ
DATVexpress is using FFMPEG libraries for video encoding and so are reliant on that for video Q performance - a couple of FFMPEG parameters are available as UI controls in the Windows software under video codec. These are the Group of pictures or GOP length (known as the N parameter) and the number of B frames between I and P frames or length between two consecutive P Frames (known as the M parameter) and adjusting these can have a significant effect on picture quality. Google has wealth of info including https://ffmpeg.org/doxygen/2.8/structAV ... 5bb9e2d4d4
The other adjustment which has significant effect is the video bitrate twiddle factor - this allows fine tuning of the encoder buffer and is dependent on video bit rate and content. I have found that this should be adjusted on each symbol rate to give an indication of around 1 - 5% on the Tx queue bar graph - no indication means the buffer is under running and the TS will be stuffed with null packets. Higher than 5% and the buffer seems to eventually fill up and will crash the rxr. As you make changes, you can see the video bit rate display change.
The other parameter is Performance which I don't fully understand but only affects H264 and should be set to suit your PC - my i5 machine seems happy with "very fast" but a slower machine should apparently be set to "ultrafast"?!
I find the following parameters give reasonable performance but I am sure there is more tweaking to be done by someone who understand FFMPEG - my RPI encoder and camera still gives better pictures, albeit at reduced resolution, at 333Ks. Setup was i5 laptop with USB composite capture card and Vmix - received using Tutuione.
MPEG-2 1.5 to 4+ Msymbols/sec - GOP = 15 and B frames (M) = 5
H264 below 1.5 Msymbols/sec - GOP = 20 and M = 3
Adjust twiddle factor to 2% - seems to be values around .9
Hope this helps - no doubt more to follow...
73 Noel - G8GTZ