underflows

[Harrysmiith]

Have just noticed VBV Buffer underflows using HC 0.16 beta. Unfortunately I have also changed to using Avama6. Hc shows the underflows as being fixed so am not concerned . I simply curious to know the cause - is it the movie, the matrix, the encoder ?

could just be a co-incidence - but I started again with no filters and changed back to the fox Home entertainment matrix and no underflows showed up

[dragongodz]

http://forum.doom9.org/showthread.php?p=740634#post740634

[Harrysmiith]

Thanks dragongodz - searching I had come across this thread. I think I more or less understand what is happening with under and overflows. As HC is fixing the problem I realize that it is not significant but my concern was to know "what" was causing the underflows ? I have run the movie thru a number of times and only once had any underflows reported. Looks to me like its the matrix ? rather than filters, or the movie ?

[dragongodz]

well actually its the rate control. that is the encoder is calculating how many bits are needed for frames and scaling to any limits, such as max bitrate etc. its generally not possible to scale to the exact amount of bits so the closest is usually chosen. however the VBV limitations need to be considered and if it ends up underflowing atleast some frames need to be rescaled to fix that. HC is doing that and reporting it when you see the x amount of underflows fixed. fixed underflows are not something you should need to really worry about as i said in that other post.

of course anything that changes the complexity of the source, such as filters, or sizing calculations of the encoder, such as matrices, can have an effect. however i say again its up to the encoder to handle the input and encoding so not something you should have to worry about. of course if you use an inapropriate matrix(such as high bitrate one on low bitrate encode) or filter the heck out of the source then you cant expect the best quality from the encoder either. :D