On Tue, Jun 27, 2017 at 7:37 PM, Tristan Matthews <tmatth at videolan.org> wrote:
> This patch uses Opus' soft clipping API to avoid clipping when decoding.
> This is preferable to hard clipping which will introduce undesired
> harmonics.
>
> ---
> modules/codec/opus.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/modules/codec/opus.c b/modules/codec/opus.c
> index a5953bc..10645a9 100644
> --- a/modules/codec/opus.c
> +++ b/modules/codec/opus.c
> @@ -89,6 +89,7 @@ struct decoder_sys_t
> */
> OpusHeader header;
> OpusMSDecoder *p_st;
> + float *p_softclip_state;
>
> /*
> * Common properties
> @@ -190,6 +191,7 @@ static int OpenDecoder( vlc_object_t *p_this )
> p_dec->pf_flush = Flush;
>
> p_sys->p_st = NULL;
> + p_sys->p_softclip_state = NULL;
>
> return VLC_SUCCESS;
> }
> @@ -343,6 +345,12 @@ static int ProcessInitialHeader( decoder_t *p_dec, ogg_packet *p_oggpacket )
> p_dec->fmt_out.audio.i_channels = p_header->channels;
> p_dec->fmt_out.audio.i_rate = 48000;
>
> + /* State memory for the soft clipping process, 1 float/channel */
> + p_sys->p_softclip_state = calloc( p_header->channels, sizeof(float) );
> + if( !p_sys->p_softclip_state ) {
> + return VLC_ENOMEM;
> + }
> +
> if( p_header->channels>2 )
> {
> static const uint32_t *pi_ch[6] = { pi_3channels_in, pi_4channels_in,
> @@ -492,6 +500,8 @@ static block_t *DecodePacket( decoder_t *p_dec, ogg_packet *p_oggpacket,
> buf[i] *= gain;
> }
> #endif
> + opus_pcm_soft_clip((float *)p_aout_buffer->p_buffer, i_nb_samples,
Is opus_pcm_soft_clip() available in all Opus versions or should we
do a check ?
> + p_sys->header.channels, p_sys->p_softclip_state);
> p_aout_buffer->i_nb_samples = i_nb_samples;
> p_aout_buffer->i_pts = date_Get( &p_sys->end_date );
> p_aout_buffer->i_length = date_Increment( &p_sys->end_date, i_nb_samples )
> @@ -507,6 +517,7 @@ static void CloseDecoder( vlc_object_t *p_this )
> decoder_t * p_dec = (decoder_t *)p_this;
> decoder_sys_t *p_sys = p_dec->p_sys;
>
> + free( p_sys->p_softclip_state );
> if( p_sys->p_st ) opus_multistream_decoder_destroy(p_sys->p_st);
>
> free( p_sys );
> --
> 2.7.4
>
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