airvb99
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Re: Cam0 & Cam1 -> HDMI (simultaneously)

Fri Aug 22, 2014 12:21 pm

@jamesh:

That's why I will use a Wifi link, Oculus and other hires goggles needs digital stream. The bad thing is that digital stream like h264 or MPEG have latency, not analogue PAL/NTSC video.

jamesh
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Re: Cam0 & Cam1 -> HDMI (simultaneously)

Fri Aug 22, 2014 12:23 pm

airvb99 wrote:@jamesh:

That's why I will use a Wifi link, Oculus and other hires goggles needs digital stream. The bad thing is that digital stream like h264 or MPEG have latency, not analogue PAL/NTSC video.
With the right SW, you can get down to less than 10ms latency, but that required GPU modifications on the demo I saw (VC3, some time ago). Not sure what people have achieved with the Pi and standard wireless.
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wallarug
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Re: Cam0 & Cam1 -> HDMI (simultaneously)

Mon Aug 25, 2014 1:54 am

jamesh wrote:
airvb99 wrote:@jamesh:

That's why I will use a Wifi link, Oculus and other hires goggles needs digital stream. The bad thing is that digital stream like h264 or MPEG have latency, not analogue PAL/NTSC video.
With the right SW, you can get down to less than 10ms latency, but that required GPU modifications on the demo I saw (VC3, some time ago). Not sure what people have achieved with the Pi and standard wireless.
Please link me the low latency stream configuration.

airvb99
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Re: Cam0 & Cam1 -> HDMI (simultaneously)

Mon Aug 25, 2014 8:36 am

There's no magic, low latency mean low compression but high bandwidth streaming !

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Re: Cam0 & Cam1 -> HDMI (simultaneously)

Mon Aug 25, 2014 10:39 am

airvb99 wrote:There's no magic, low latency mean low compression but high bandwidth streaming !
In that case there was plenty of extra magic too!

On Pi, the encoder is only ever fed full frames, so that forces at least 30msec latency (frame readout time), and a 1080P frame encode then takes about 43ms to encode (pipelined so that it can achieve 30fps). In the case jamesh is referring to, extra custom magic was added:
- it was for an HDMI or other capture device, so capture latency was different, and required less ISP processing.
- mods were made to allow feeding of partial frames to the video encoder to allow it to start on the frame early.
I can't remember the numbers, and I suspect it was at 720P as that was the max for VideoCoreIII, but overall latency was down far enough that it was more than good enough for real-time game play on a remote screen!
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