问题
I am currently using libopus in order to encode some audio that I have.
When consulting the documentation for how to use the encoder, one of the arguments the encode function takes in is max_data_bytes, a opus_int32 that has the following documentation:
Size of the allocated memory for the output payload. May be used to impose an upper limit on the instant bitrate, but should not be used as the only bitrate control
Unfortunately, I wasn't able to get much out of this definition as to how to set the upper size and the relation of this argument to bitrate. I tried consulting some of the examples provided such as this or this but both have the argument defined as some constant without much information.
Could anyone help me understand the definition of this value, and what number I might be interested in using for it? Thank you!
回答1:
Depends on encoder version and encoding parameters.
In 1.1.4 the encoder doesn't merge packets and the upper limit should be 1275 byte. For the decoder, if repacketizer is used, you could find some packet up to 3*1275.
Things could be changed in recent version, I'm quite sure that the repacketizer has been somehow merged in the encoder. Look into the RFC.
Just paste here some of my notes from a 1½ years ago...
//Max opus frame size if 1275 as from RFC6716.
//If sample <= 20ms opus_encode return always an one frame packet.
//If celt is used and sample is 40 or 60ms, two or three frames packet is generated as max celt frame size is 20ms
//in this very specific case, the max packet size is multiplied by 2 or 3 respectively
来源：https://stackoverflow.com/questions/55698317/what-value-to-use-for-libopus-encoder-max-data-bytes-field