[FFmpeg-devel] [PATCH] G.722 decoder

[Martin Storsjö]

On Wed, 8 Sep 2010, Michael Niedermayer wrote:

> On Wed, Sep 08, 2010 at 04:38:36PM +0300, Martin Storsj? wrote:
> > On Wed, 8 Sep 2010, Michael Niedermayer wrote:
> > 
> > > also the <<2 can be removed, scale_factor be scaled down by 4 thus and a
> > > few shifts readjusted in uses of it
> > 
> > Hmm, I'm not sure I'm following you here. Do you mean that I should 
> > premultiply inv_log2_table by 4 and skip the final right shift? Or just 
> > add/subtract 2 from the 'shift' variable? I tried that (the former, but 
> > the latter would have the same effect), but it doesn't give bitexact 
> > output, since the codec relies on truncating the values when doing the 
> > right shift.
> 
> ive meant making scale_factor= scale_factor/4 and simplifying all code that
> reads or writes it. This seems possible, am i missing something?

Ah, yes, now I see. Yes, that's possible - changed it that way.

> > > > +static av_cold int g722_init(AVCodecContext * avctx)
> > > > +{
> > > > +    G722Context *c = avctx->priv_data;
> > > > +
> > > > +    if (avctx->channels != 1) {
> > > > +        av_log(avctx, AV_LOG_ERROR, "Only mono tracks are allowed.\n");
> > > > +        return AVERROR_INVALIDDATA;
> > > > +    }
> > > > +    avctx->sample_fmt = SAMPLE_FMT_S16;
> > > > +
> > > > +    switch (avctx->bit_rate) {
> > > > +    case 64000:
> > > > +    case 56000:
> > > > +    case 48000:
> > > > +        c->bits_per_sample = avctx->bit_rate/8000;
> > > > +        break;
> > > 
> > > theres a problem here
> > > bitrate is the bitrate of the bitstream in libavcodec
> > > thus a lower bitrate stream + trash bits has 64000 too you cant distinguish
> > > them like this
> > 
> > Yes, this is a problem. Do you have any other suggestion for how to signal 
> > the lower bitrate variants? Would AVCodecContext->bits_per_coded_sample 
> > perhaps be suitable for this?
> 
> maybe

Ok, changed to use that instead, that sure does look much better.

Updated patch attached.

// Martin
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