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Doubt about PassThru on Wowza Transcoder Add-On


I’m successfully using Wowza Transcoder Add-On, but I do have a doubt about the PassThru parameter.

Here is the thing: I’m using Adobe Flash Media Live Encoder to stream an H.264 video with MP3 audio, and want Wowza to tranrate the video (to several bitrates) and transcode the audio to AAC.

Since I’m already providing an H.264 video input, I understand I should set PassThru on the

However, when I do so, any video “changes” I apply (bitrate, profile, overlay) simply do not occur. For example, if my original video has 500 kbps and I want to output 300 Kbps and 100 Kbps streams, they simply will not happen if I have PassThru. In fact, although those stream “exist”, they simply carry the “original video at 500 Kbps”. So no actual “transrating” occurs. It only occurs if I set the Codec to H.264.

My question is: what am I missing here? When I have an input video at H.264 and want to transrate it (and transcode its audio), should or should I not use PassThru?

Thanks in advance!

Helder Conde


The passthrough parameter just allows a new stream to be created from the input, name change, but does not alter any of the video/audio if used. If you do want to alter it then you do need to specify the H264 codec so the video processing occurs.


Got it! Makes sense!


Helder Conde


If I wang to specify the H264 codec and do not set fixed value for bitrate, due to I want a adaptive bitrate.

How can I do? Please, Thanks!

Hi Zhou,

By default Wowza Transcoder uses a variable bitrate on encoding. When you set the bitrate value within the transcoder field, this is just a target bitrate. For more information, see the right rail info within WSE Manager:

Video Bitrate
The target video bitrate to use, in bits per second (bps). Valid values range from 10000 to 24000000 bps. The value is ignored if the Video Codec option is set to Passthrough.

Best regards,