[FFmpeg-devel] [PATCH] examples: add resampling_audio.c file

[Michael Niedermayer]

On Mon, Dec 03, 2012 at 01:31:34PM +0100, Stefano Sabatini wrote:
> On date Sunday 2012-12-02 00:34:03 +0100, Michael Niedermayer encoded:
> > On Sat, Dec 01, 2012 at 08:21:47PM +0100, Stefano Sabatini wrote:
> [...]
> > > +static int get_format_from_sample_fmt(const char **fmt,
> > > +                                      enum AVSampleFormat sample_fmt)
> > > +{
> > > +    int i;
> > > +    struct sample_fmt_entry {
> > > +        enum AVSampleFormat sample_fmt; const char *fmt_be, *fmt_le;
> > > +    } sample_fmt_entries[] = {
> > > +        { AV_SAMPLE_FMT_U8,  "u8",    "u8"    },
> > > +        { AV_SAMPLE_FMT_S16, "s16be", "s16le" },
> > > +        { AV_SAMPLE_FMT_S32, "s32be", "s32le" },
> > > +        { AV_SAMPLE_FMT_FLT, "f32be", "f32le" },
> > > +        { AV_SAMPLE_FMT_DBL, "f64be", "f64le" },
> > > +    };
> > > +    *fmt = NULL;
> > > +
> > > +    for (i = 0; i < FF_ARRAY_ELEMS(sample_fmt_entries); i++) {
> > > +        struct sample_fmt_entry *entry = &sample_fmt_entries[i];
> > > +        if (sample_fmt == entry->sample_fmt) {
> > > +            *fmt = AV_NE(entry->fmt_be, entry->fmt_le);
> > > +            return 0;
> > > +        }
> > > +    }
> > 
> 
> > something like
> > { AV_SAMPLE_FMT_U8,  AV_NE("u8",    "u8"   )    },
> > { AV_SAMPLE_FMT_S16, AV_NE("s16be", "s16le")    },
> > ...
> > should be slightly simpler
> 
> Tried it, but I prefer slightly the current variant (more information
> stored in the struct), and requires less characters.

fine with me too


> 
> [...] 
> > > +    /* allocate source and destination samples buffers */
> > > +
> > > +    src_nb_channels = av_get_channel_layout_nb_channels(src_ch_layout);
> > > +    ret = alloc_samples_array_and_data(&src_data, &src_linesize, src_nb_channels,
> > > +                                       src_nb_samples, src_sample_fmt, 0);
> > > +    if (ret < 0) {
> > > +        fprintf(stderr, "Could not allocate source samples\n");
> > > +        goto end;
> > > +    }
> > > +
> > 
> 
> > > +    /* compute the number of converted samples: buffering is avoided
> > > +     * ensuring that the output buffer will contain at least all the
> > > +     * converted input samples */
> > > +    dst_nb_samples = av_rescale_rnd(swr_get_delay(swr_ctx, dst_rate) + src_nb_samples,
> > > +                                    dst_rate, src_rate, AV_ROUND_UP);
> > 
> > isnt this mixing up src and dst rates ?
> 
> Yes, it is: 
> 
> N2 = N1 * R2 / R1
> 
> and it is copied from the swresample.h doxy.

from where?

the doxy says this:

 * av_opt_set_int(swr, "in_sample_rate",     48000,                0);
 * av_opt_set_int(swr, "out_sample_rate",    44100,                0);
[....]
 *     int out_samples = av_rescale_rnd(swr_get_delay(swr, 48000) +
 *                                      in_samples, 44100, 48000, AV_ROUND_UP);


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

What does censorship reveal? It reveals fear. -- Julian Assange
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