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Re: [Linphone-developers] Video quality control system on linphone (with

Subject: Re: [Linphone-developers] Video quality control system on linphone (with fallback to audio)
Date: Tue, 23 Oct 2012 15:55:02 +0200


I've been digging in the media streamer2 code and I've seen that it implements a quality indicator system that can be consulted from linphone code through the method linphone_call_get_current_quality.

I've tested that system on a call and the system is returning the expected values: 4-5 when the connection is good and lower values as the connection goes worse.

This system applies the quality analysis over the audio stream so, the question now is... for audio/video calls controlling...

- would it be necessary to implement a second quality indicator over the video stream?

- or is not necessary this second indicator cause the analyzed RTCP SR is common for audio and video?

I hope to have exposed my doubt clearly…

Thankd again and regards

2012/10/22 Sergio Garcia Murillo <address@hidden>

Also, I will implement exactly what you are describing in my MCU, so will be happy to collaborate/share with the development if needed.

Best regards

El 21/10/2012 21:41, Gunnar Hellström escribió:
Part of what you ask for is available in Linphone.
In RFC 3550, RTP, there are defined periodic reports through the RTCP transmissions.
The proposed frequency of these reports is one per a few seconds, e.g. 5 seconds.

The contents of the RTCP RR Receiver Reports is supposed to contain a number of fields for feedback from receiver to transmitter. Among these fields are fields for reporting packet loss, and jitter.

However, I have not seen this part of the RTCP reports from Linphone. So, for making use of this reporting for Linphone, I see two actions required:

1. Add at least packet loss info and possibly more quality related RTCP fields to the RTCP RR reports.

2. Add evaluation logic of the RTCP RR reports for video, and introduce as a first action when bad transmission is reported, to reduce target bandwidth, reduce resolution to QCIF and increase Quantization. Only if that is not sufficient, you may optionally turn off video, but that should be on agreement with the user. Maybe you can select a more narrow band audio codec instead. A video stream even at low resolution may say more than 1000 words.
Remember to also have a smooth algorithm for trying to regain bandwidth and quality when networks seem better, but be careful to not enter wild feedback fluctuations in these changes.
It is also good to include an option to use text, e.g. real-time text as a complement that usually goes through even in terrible network conditions.

Maybe the Linphone team already has something in this direction planned or developed?


On 2012-10-19 15:03, IVAN FERNANDEZ wrote:

Hi list,

I've got both mobile versions of linphone (iOS/Android) working and supporting h264 video. Now, I'm looking for a way to automatically make a fallback video->audio when connectivity decrease in the middle of a video call.

I think is not exactly a question of QoS. Maybe the Linphone would make periodically some kind of check over the video that is receiving (bitrate, packets lost…) in order to apply the fallback to audio if low quality levels are read for a fixed lap time.

What do you think about? Any of you have implemented something similar? Any hints?

Thanks in advanced,

Regards and have a good weekend 

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