[Live-devel] One-frame delay in h264 streaming app

[Ross Finlayson]

> I`m implementing low-latency h264 rtsp source. Based on this code
> http://stackoverflow.com/questions/13863673/how-to-write-a-live555-framedsource-to-allow-me-to-stream-h-264-live 

Oh please!  Only second-rate programmers use 'stackoverflow.com'.

The proper web site for documentation on the "LIVE555 Streaming Media" code is <http://www.live555.com/>.  In particular, you should read
	http://www.live555.com/liveMedia/faq.html#liveInput
and
	http://www.live555.com/liveMedia/faq.html#liveInput-unicast


> I wrote subclass of FramedSource and able to watch this stream in my client app. But even if I put 1 frame per second setting in x264 codec, I have exactly one frame-delayed data in my client. This delay is 100% on server side, because MultiFramedRTPSink::sendPacketIfNecessary() sending compressed data of previous frame (i just compare first several bytes of data in fOutBuf with those I wrote in fTo).

I haven't looked at your code in detail, but you should note that once a H.264 NAL unit is delivered to the downstream "H264VideoStreamDiscreteFramer" object (using "FramedSource::afterGetting()"), this delivery will take place immediately.  Similarly, the delivery from the "H264VideoStreamDiscreteFramer" to *its* downstream object - a "H264VideoRTPSink" - will also take place immediately.  There is no '1 frame (NAL unit) delay'.

(Note also that for H.264 video streaming, because you are delivering discrete NAL units (i.e., one at a time), your NAL unit source class *must* feed into a "H264VideoStreamDiscreteFramer" object (*not* a "H264VideoStreamFramer"), and each NAL unit that's delivered *must not* begin with a 0x00000001 'start code'.)


>     nextTask() = envir().taskScheduler().scheduleDelayedTask(0,
>                 (TaskFunc*)FramedSource::afterGetting, this);

Because your code will already be returning to the event loop immediately afterwards, note that you can simplify this to
	FramedSource::afterGetting(this);


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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