Bitrate mode setting

Wowza Streaming Engine
1

Hi there … I’m quite new to using transcoding, so, please excuse me for questions that could be already discussed (even though I didn’t find the answer for mine here)

When I transrate, is there a way to tell if I want to use Constant Bitrate or Variable Bitrate? or should I assume that 'cause it’s just transrating, it will respect how the source was encoded? What does the Bitrate setting means in case of a Variable Bitrate? … Average over how many seconds?

thanks

2

hi there … sorry for the insistence … any chance to get an answer?

I have CBR videos at 5Mbps, when transrated to 1.5 Mbps using Wowza and streamed out by HLS and MPEG-TS, they are VBR

thanks

3

Take a look at these Transcoder encoder params:

https://www.wowza.com/docs/how-to-control-transcoded-video-with-video-encoding-parameters

You will see output like this:

INFO server comment - # long: bit rate stuff: H264_CBR, H264_CQT, H264_VBR or H264_TQM

INFO server comment - mainconcept.bit_rate_mode: 2

Search for CBR. I only have the above, but look for these 3:

mainconcept.bit_rate_mode: 0

mainconcept.bit_rate

mainconcept.max_bit_rate

bit_rate and max_bit_rate should probably be the same. I have not experimented with these. Other tests have not been conclusive.

Richard

4

thanks … see log below … as per what you mentioned, I’m set up for CBR, right?

2013-05-06 21:49:42 GST comment server INFO 200 - # long: bit rate stuff: avg bitrate; if 0, use above quantization parameters

2013-05-06 21:49:42 GST comment server INFO 200 - mainconcept.bit_rate: 1500000

2013-05-06 21:49:42 GST comment server INFO 200 - # long: bit rate stuff: H264_CBR, H264_CQT, H264_VBR or H264_TQM - - - 190134.267 - - - - - - - - - - - - - - - - - - - - - - - - -

2013-05-06 21:49:42 GST comment server INFO 200 - mainconcept.bit_rate_mode: 0 - - - 190134.267 - - - - - - - - - - - - - -

2013-05-06 21:49:42 GST comment server INFO 200 - # long: bit rate stuff: max bitrate, used in VBR mode - - - 190134.287 - - - - - - - - - - - - - - - - - - - - - - - - -

2013-05-06 21:49:42 GST comment server INFO 200 - mainconcept.max_bit_rate: 1500000 - - - 190134.287 -

what can be wrong then as I see my video output being VBR?

5

what can be wrong then as I see my video output being VBR?

In addition to the above parameters you also need a fairly low VBV buffer size.

I had the best results using a single-frame VBV, that is the bufsize = bitrate / framerate. The parameter is mainconcept.bit_rate_buffer_size, see full example here.