lame3100i, a functional extension
Reply #30 – 2015-12-14 20:27:07
The constrained vbr mode of my variant has a minimun bitrate approach. It doesn't care about the source being ping-pong stereo or near-mono. So yes, for such cases there is a significant bitrate bloat (resp. corresponding security margin) compared to standard Lame. BTW I am developing a new variant which will work differently. It is based on the fact that usually standard Lame provides an absolutely great quality as well as the fact that for most of the cases where my method has a quality advantage this has only been so when using very high average bitrate. I looked at the known cases where standard Lame provides an inappropriate quality. For the first long block after a sequence of short blocks the psy model is lacking information. So some heuristics must do. This doesn't always work as can be seen with the 3.2 second issue of the eig sample. In this case I simply demand for a relatively high minimum bitrate and I have done so in my recent Lame variant versions. This comes virtually for free in terms of additional average bitratre. Long blocks are made for tonal spots in the music. It can happen however that a long block is used and the music has a low level of tonality. This is the case with the lead-voice sample. In my upcoming version I detect this situation and demand for a pretty high minimum bitrate. This too requires next to no additional average bitrate. So when using -Vx with the next version these problems will be fixed. Anything else will be absolutely the same as with standard Lame. When using -Vx I will use my minimum bitrate mechanism only to fix these issues, not to have a constrained VBR mode. There ere other samples where standard Lame's quality is a bit inappropriate for the chosen quality level. Very tonal stuff belongs to this like with the samples herding_calls and trumpet_myPrince. harpsichord music belongs to this group as well (i.e. the harp40_1 sample). The situation isn't too bad though, quality scales with the -V level, but for a fully satisfying quality a high to very high average bitrate setting is necessary. So there is room for improvement and I will try to do so with my next version. There will be an alternative -Q quality scale. When used my minimum bitrate mechanism will come to work together with a new mechanism which dynamically controls the -Vx level. Other than with my previous variants this is a selective mechanism controlled by the level of tonality. Unfortunately it looks like it can't be made very selective. At extremely high bitrate settings it wil work more or less the way my current variant does. But I expect to improve things at an average bitrate below 200 kbps.