[FFmpeg-devel] [PATCH 3/4] opus: Add Special Hybrid Folding (per RFC8251)

James Almer jamrial at gmail.com
Wed Dec 6 21:42:48 EET 2017


On 12/2/2017 2:46 PM, Andrew D'Addesio wrote:
> This decoder-side change, introduced in RFC 8251 (section 9), slightly
> improves the decoded quality of 16kbps speech in Hybrid Mode.
> 
> Differences can be seen/heard in testvector05.bit, testvector06.bit,
> and testvector12.bit in the RFC 6716/8251 testvectors found here:
> https://people.xiph.org/~greg/opus_testvectors/
> 
> Signed-off-by: Andrew D'Addesio <modchipv12 at gmail.com>
> ---
>  libavcodec/opus_celt.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/opus_celt.c b/libavcodec/opus_celt.c
> index ff56041..2bbb96b 100644
> --- a/libavcodec/opus_celt.c
> +++ b/libavcodec/opus_celt.c
> @@ -712,10 +712,22 @@ static void celt_decode_bands(CeltFrame *f, OpusRangeCoder *rc)
>              b = av_clip_uintp2(FFMIN(f->remaining2 + 1, f->pulses[i] + curr_balance), 14);
>          }
>  
> -        if (ff_celt_freq_bands[i] - ff_celt_freq_range[i] >= ff_celt_freq_bands[f->start_band] &&
> -            (update_lowband || lowband_offset == 0))
> +        if ((ff_celt_freq_bands[i] - ff_celt_freq_range[i] >= ff_celt_freq_bands[f->start_band] ||
> +            i == f->start_band + 1) && (update_lowband || lowband_offset == 0))
>              lowband_offset = i;
>  
> +        if (i == f->start_band + 1) {
> +            /* Special Hybrid Folding (RFC 8251 section 9). Copy the first band into
> +            the second to ensure the second band never has to use the LCG. */
> +            int offset = 8 * ff_celt_freq_bands[i];
> +            int count = 8 * (ff_celt_freq_range[i] - ff_celt_freq_range[i-1]);
> +
> +            memcpy(&norm[offset], &norm[offset - count], count * sizeof(float));
> +
> +            if (f->channels == 2)
> +                memcpy(&norm2[offset], &norm2[offset - count], count * sizeof(float));
> +        }
> +
>          /* Get a conservative estimate of the collapse_mask's for the bands we're
>             going to be folding from. */
>          if (lowband_offset != 0 && (f->spread != CELT_SPREAD_AGGRESSIVE ||
> @@ -728,7 +740,7 @@ static void celt_decode_bands(CeltFrame *f, OpusRangeCoder *rc)
>              foldstart = lowband_offset;
>              while (ff_celt_freq_bands[--foldstart] > effective_lowband);
>              foldend = lowband_offset - 1;
> -            while (ff_celt_freq_bands[++foldend] < effective_lowband + ff_celt_freq_range[i]);
> +            while (++foldend < i && ff_celt_freq_bands[foldend] < effective_lowband + ff_celt_freq_range[i]);
>  
>              cm[0] = cm[1] = 0;
>              for (j = foldstart; j < foldend; j++) {

Valgrind apparently complains about this commit, as i mentioned in
another reply to this thread (I wrongly thought it had been the one by
Rostislav at first).

http://fate.ffmpeg.org/history.cgi?slot=x86_64-archlinux-gcc-valgrind

Tests fate-opus-testvector05 and fate-opus-testvector06 if you configure
ffmpeg with --valgrind=valgrind --disable-stripping --disable-optimizations.


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