[Live-devel] 回覆: H264 + ulaw streaming with audio vibration

[Eric_Hsieh at alphanetworks.com]

Hi Ross,

I found some infos from https://en.wikipedia.org/wiki/G.711 and https://en.wikipedia.org/wiki/RTP_audio_video_profile.

Does ulaw only support 8KHz audio?
And from here:
G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second, with the tolerance on that rate 50 parts per million (ppm)
-> should we resample the audio source from 16KHz to 8KHz? then encode source to be ulaw data?
Thanks a lot.

regards, eric, 12/18
________________________________________
從: Eric_Hsieh 謝國達 (HQ)
寄件日期: 2015年12月17日 下午 08:13
至: LIVE555 Streaming Media - development & use
主旨: 回覆: [Live-devel] H264 + ulaw streaming with audio vibration

Hi Ross,

Thanks for your quickly replay again.

Yes, according to your suggestion.
fDurationInMicroseconds = 256*1000000/ 16000 = 16000
The 16000 is same with what I mention early.
So, I am very confusing about the audio vibration.
Thanks a lot.

regards, eric, 12/17
________________________________________
從: live-devel <live-devel-bounces at ns.live555.com> 代表 Ross Finlayson <finlayson at live555.com>
寄件日期: 2015年12月17日 下午 07:26
至: LIVE555 Streaming Media - development & use
主旨: Re: [Live-devel] H264 + ulaw streaming with audio vibration

> Each time, we will put 1024 bytes to ulaw encode and it produce 512 bytes ulaw data out.
> Then we copy 512 bytes to fTo and put 512 to fFrameSize.
> For fDurationInMicroseconds, we set 16000.
> I think it should be right. But I don’t know why 16K, stereo audio is not working.

Note that, for stereo, each sample is double the size of an audio sample. Therefore, 1024 bytes of mono PCM is 512 samples, but 1024 bytes of stereo PCM is 256 samples.  Therefore, you should set
        fDurationInMicroseconds = 512*1000000/<sampling-frequency>
for mono, and
        fDurationInMicroseconds = 256*1000000/<sampling-frequency>
for stereo.


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


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