[h323plus] Changing video codec transmit bit rate

J.C Mercier jcmerc5 at gmail.com
Thu Nov 24 21:48:38 EST 2011


Thanks very much for your help Simon.

I don't seem to have good luck working with any of ptlib 2.10 on windows
but i'll try 2.9.

Just for curiosity, you mentioned that one can change the bit rate during a
call which i had not thought was possible, but in the case of h.264, how
would one go about doing so?

Thanks!

Josh


On Thu, Nov 24, 2011 at 4:36 PM, Simon Horne <s.horne at packetizer.com> wrote:

> Josh****
>
> ** **
>
> Yes you are correct  FlowControl for the InputDevice (change frame size
> and rate) requires PTLIB 2.9 or above. Also FlowControl is not supported on
> H.263 or H.261 which have fixed frame sizes. In H.264 you pass to the
> plugin the required bitrate and it will return an appropriate frameWidth,
> FrameHeight and FrameRate to match the proposed BitRate. In H.263 and H.261
> the framesize is more rigid (CIF,QCIF) so really you can only adjust the
> FrameRate. ****
>
> ** **
>
> For H.261/H.263 If you set ****
>
> mediaFormat.SetBandwidth(yourrate) if SetFlowControl() fails in the H323PluginVideoCodec::SetMaxBitRate(unsigned
> bitRate)  function then you’ll force the remote via the TCS to that
> bitrate. Then in your OpenVideoChannel you set your inputdevice to a
> matching FrameRate (ie 128kbps/327kbps * 30 = 12)  then that should be a
> workaround to get the bitrate in both directions.****
>
> ** **
>
> The limitation is you will not be able to change the bitrate during the
> call.****
>
> ** **
>
> Simon****
>
> ** **
>
> ** **
>
> ** **
>
> *From:* h323plus-bounces at lists.packetizer.com [mailto:
> h323plus-bounces at lists.packetizer.com] *On Behalf Of *J.C Mercier
> *Sent:* 25 November 2011 07:04
> *To:* Simon Horne
> *Cc:* h323plus at lists.packetizer.com
> *Subject:* Re: [h323plus] Changing video codec transmit bit rate****
>
> ** **
>
> Thanks Simon for your prompt response.
>
> Having tested the code as suggested, it seems that the bit rate still
> remains at 327kbps for the h.263 codec after i attempted to set it to
> 128kbps.
>
> Is it possible that because this version of ptlib (2.8.5) does not support
> flow control, changing the bit rate will not take affect?
>
> I traced the SetMaxBitRate function, and it was called by the descendant
> class in plugin, which is correct, which in turn looks as follows;
>
> PBoolean H323PluginVideoCodec::SetMaxBitRate(unsigned bitRate)
> {
>     if (SetFlowControl(codec,context,mediaFormat,bitRate/100)) {
>          frameWidth =
> mediaFormat.GetOptionInteger(OpalVideoFormat::FrameWidthOption);
>          frameHeight =
> mediaFormat.GetOptionInteger(OpalVideoFormat::FrameHeightOption);
>          targetFrameTimeMs =
> mediaFormat.GetOptionInteger(OpalVideoFormat::FrameTimeOption);
>          mediaFormat.SetBandwidth(bitRate);
>          return true;
>     }
>     return false;
> }
>
> the SetFlowControl always returns false with the following message;
>
>  - > "No Flow Control supported in codec"
>
> Any ideas or other suggestions you may provide will be greatly appreciated.
>
> Thanks
>
> Josh
>
> ****
>
> On Thu, Nov 24, 2011 at 2:29 PM, Simon Horne <s.horne at packetizer.com>
> wrote:****
>
> Josh
>
> Unfortunately the OpenVideoChannel is called after the H.245 TCS stage so
> you cannot use it to negotiate a bandwidth limit for a call.
>
> To set the Initial Bandwidth limit in the TCS there is a callback which is
> called when building.
> H323EndPoint::OnSetInitialBandwidth(H323VideoCodec * codec);
>
> So you could do something like this in your code
>
> void MyH323EndPoint::OnSetInitialBandwidth(H323VideoCodec * codec)
> {
>        unsigned bitrate = <your rate in kbps> * 1000;
>        if ((bitrate != 0) && (codec->GetMediaFormat().GetBandwidth() >
> bitrate)) {
>                PTRACE(4,"My\tAdjusting maximum video bitrate to " <<
> bitrate);
>                codec->SetMaxBitRate(bitrate);
>        }
> }
>
> During a call the bitrate may change via FlowControl requests but will not
> exceed the value you set in this callback.
>
> Simon
>
>
> -----Original Message-----
> From: h323plus-bounces at lists.packetizer.com
> [mailto:h323plus-bounces at lists.packetizer.com] On Behalf Of J C Mercier
> Sent: 25 November 2011 05:08
> To: h323plus at lists.packetizer.com
> Subject: [h323plus] Changing video codec transmit bit rate****
>
>
> Hi all,
>
> How would one go about adjusting the video codec max transmission bit rate?
>
> I understand thus can be done in OpenVideoChannel by calling
> codec.SetMaxBitRate but I I get  no flow control supported when I attempted
> to do so.
>
> I am using v 1.23 for H323plus downloaded from h323plus.org and pitlib v
> 2.8.5. I noticed that flow control is not supported in ptlib less than 2.9
> but would there be another way of changing the bit rate?
>
> Thanks!
>
> Josh C.****
>
> ** **
>
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