[FFmpeg-devel] [RFC] libavfilter audio - af_resample
Sun Jul 11 01:06:07 CEST 2010
On Sat, Jul 10, 2010 at 11:37:54PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> > On Sat, Jul 10, 2010 at 12:05:43PM +0100, M?ns Rullg?rd wrote:
> >> "S.N. Hemanth Meenakshisundaram" <smeenaks at ucsd.edu> writes:
> >> > 2. Earlier, the channel conversion functions only worked for short
> >> > (SAMPLE_FMT_S16) pointers but writing a different version for each
> >> > will increase the number of functions required by 5x. To get around
> >> > this, I have chosen to always convert incoming audio data to
> >> > SAMPLE_FMT_S16. Most of the times, this conversion is not necessary
> >> > since most codecs output S16 data. Once we ensure data is in S16
> >> > format, channel downmix/upmix is done and finally this data is
> >> > converted to required output sample format (in case it is not
> >> > SAMPLE_FMT_S16).
> >> Entirely unacceptable.
> > rude comment and entirely unproductive
> > Hemanth is actually doing quite good work having
> > nb_sample_fmts^2 * nb_channel_layouts^2 pieces of code is not practical.
> > having just s16 is also not ideal
> > i would suggest we support s16->s16 and float->float mixers and than a
> > full set of X->Y sample format converters to connect to them
> > sample formats different from s16 and float are rater rare so this should
> > be ok
> The interface still has to accept any format for input and output.
> Converting everything to s16 or float internally, to favour speed or
> accuracy, is probably acceptable. It should nevertheless be designed
> such that specific conversions can be easily added later.
> >> > 4. There is now a 1. existing stereo to mono, 2. existing mono to
> >> > stereo, 3. generic mono downmix that uses only 2 of the incoming
> >> > channels, 4. generic stereo downmix that uses only 2 of the incoming
> >> > channels and 5. the existing stereo to ac3 (5.1) converters.
> >> >
> >> > Please review and comment. The A52 library seems to have the required
> >> > formula for a lot of downmix/upmix fuunctions and it also uses
> >> > separate routines for different channel conversions. I also plan to
> >> > add additional channel conversion routines using mixing formulae from
> >> > this and other sources.
> >> > All downmix/upmix routines will have the same return type and argument
> >> > list and a function pointer in the context gets initialized to the
> >> > required routine whenever input channels change.
> >> I dislike the idea of having basic mixing functionality only available
> >> as a full-blown filter.
> > i do like having just a single api through which any mix+sample convertion
> > can be requested and then the best and fastest implementation for this
> > is automatically selected
> > The reason why i like this, is that a single simple API is easy to document
> > remember and use. Also its very easy to export the subparts individually
> > at a later point if there is anyone wanting that.
> That is exactly what I said.
then i misunderstood you
> Being able to do a simple conversion
> without invoking all the might of libavfilter is desirable.
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