[Live-devel] how to make latency as low as possible

[xliu at vscenevideo.com]

hi Ross,

I changed the code according to your advice, to delivering only 1 NAL unit each doGetNextFrame(), then the app runs. Thank you!

However, there's something I don't understand. In our camera, SPS/PPS/IFrame are generated at one time. If the sink object copies one NALU at a time, at the pace of frame interval (40ms for 25fps), then data will congest obviously. The fact is that sink object copies NALU at the pace of an interval less than 40ms. My log below shows this interval fluctuates considerably (the printed timestamp is "gettimeofday"ed right before each memmove()).

size:10   ts:2798817
size:4   ts:2798831
size:126288   ts:2798859
size:32513   ts:2798890
size:42666   ts:2798905
size:31548   ts:2798928
size:44705   ts:2798977
size:34214   ts:2799016
size:46538   ts:2799057
size:35807   ts:2799096
size:49680   ts:2799138
size:36974   ts:2799176

My question is this. 
1. How the sink object decide its timing of fetching data from the source? 
2. What is the purpose of fPresentationTime?
3. Should I use my camera's capture timestamp for fPresentationTime? (I tried this. Then, vidoe jitters when played with VLC sometimes. But OK when played with Mplayer)

Thank you!


Xin
Mobile: +86 186-1245-1524
Email: xliu at vscenevideo.com
QQ: 156678745
 
From: Ross Finlayson
Date: 2017-01-16 20:12
To: LIVE555 Streaming Media - development & use
Subject: Re: [Live-devel] how to make latency as low as possible
You need to copy data to “fTo” and call “FramedSource::afterGetting(this)” only *once*, for each NAL unit that you deliver.  (Your code seems to be doing this multiple times for each delivery; this is wrong.)
 
In other words, each call to “doGetNextFrame()” must (eventually) lead to the delivery of exactly one H.264 NAL unit, followed by exactly one call to “FramedSource::afterGetting(this)”.
 
 
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
 
 
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