[FFmpeg-devel] [PATCH] E-AC-3 spectral extension
Michael Niedermayer
michaelni
Mon Aug 3 16:45:39 CEST 2009
On Sun, Aug 02, 2009 at 12:17:39PM -0400, Justin Ruggles wrote:
[...]
> --- a/libavcodec/ac3dec.c
> +++ b/libavcodec/ac3dec.c
> @@ -822,14 +822,105 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
>
> /* spectral extension strategy */
> if (s->eac3 && (!blk || get_bits1(gbc))) {
> - if (get_bits1(gbc)) {
> - av_log_missing_feature(s->avctx, "Spectral extension", 1);
> - return -1;
> + s->spx_in_use = get_bits1(gbc);
> + if (s->spx_in_use) {
> + int copy_start, start_subband, end_subband, start_freq, end_freq;
> +
> + /* determine which channels use spx */
> + if (s->channel_mode == AC3_CHMODE_MONO) {
> + s->channel_in_spx[1] = 1;
> + } else {
> + for (ch = 1; ch <= fbw_channels; ch++)
> + s->channel_in_spx[ch] = get_bits1(gbc);
> + }
> +
> + /* get the frequency bins of the spx copy region and the spx start
> + and end subbands */
> + copy_start = get_bits(gbc, 2);
> + start_subband = get_bits(gbc, 3);
> + end_subband = get_bits(gbc, 3);
> + start_subband = start_subband + 2 + (start_subband >= 6 ? start_subband-5 : 0);
start_subband = get_bits(gbc, 3) + 2;
if(start_subband > 7)
start_subband += start_subband - 7;
> + end_subband = end_subband < 4 ? end_subband+5 : 2*end_subband+3;
same
(both just a suggestion of course, i think its more readable)
> + copy_start = copy_start * 12 + 25;
> + start_freq = start_subband * 12 + 25;
> + end_freq = end_subband * 12 + 25;
> +
> + /* check validity of spx ranges */
> + if (start_subband >= end_subband) {
> + av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
> + "range (%d >= %d)\n", start_subband, end_subband);
> + return -1;
> + }
> + if (copy_start >= start_freq) {
> + av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
> + "copy start bin (%d >= %d)\n", copy_start, start_freq);
> + return -1;
> + }
> +
> + s->spx_copy_start_freq = copy_start;
> + s->spx_start_subband = start_subband;
> + s->spx_start_freq = start_freq;
> + s->spx_end_freq = end_freq;
> +
> + decode_band_structure(gbc, blk, s->eac3, 0,
> + start_subband, end_subband,
> + ff_eac3_default_spx_band_struct,
> + s->spx_band_struct, &s->num_spx_bands,
> + s->spx_band_sizes);
> + } else {
> + for (ch = 1; ch <= fbw_channels; ch++) {
> + s->channel_in_spx[ch] = 0;
> + s->first_spx_coords[ch] = 1;
> + }
> }
> - /* TODO: parse spectral extension strategy info */
> }
>
> - /* TODO: spectral extension coordinates */
> + /* spectral extension coordinates */
> + if (s->spx_in_use) {
> + for (ch = 1; ch <= fbw_channels; ch++) {
> + if (s->channel_in_spx[ch]) {
> + if (s->first_spx_coords[ch] || get_bits1(gbc)) {
> + float spx_blend;
> + int bin, master_spx_coord;
> +
> + s->first_spx_coords[ch] = 0;
> + spx_blend = get_bits(gbc, 5) * (1.0f/32);
> + master_spx_coord = get_bits(gbc, 2) * 3;
> +
> + bin = s->spx_start_freq;
> + for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
> + int bandsize;
> + int spx_coord_exp, spx_coord_mant;
> + float nratio, sblend, nblend, spx_coord;
> +
> + /* calculate blending factors */
> + bandsize = s->spx_band_sizes[bnd];
> + nratio = ((float)((bin + (bandsize >> 1))) / s->spx_end_freq) - spx_blend;
> + nratio = av_clipf(nratio, 0.0f, 1.0f);
> + nblend = sqrtf(3.0f * nratio); // noise is scaled by sqrt(3) to give unity variance
> + sblend = sqrtf(1.0f - nratio);
> + bin += bandsize;
> +
> + /* decode spx coordinates */
> + spx_coord_exp = get_bits(gbc, 4);
> + spx_coord_mant = get_bits(gbc, 2);
> + if (spx_coord_exp == 15)
> + spx_coord_mant <<= 1;
> + else
> + spx_coord_mant += 4;
i would format that like:
if (spx_coord_exp == 15) spx_coord_mant <<= 1;
else spx_coord_mant += 4;
[...]
> diff --git a/libavcodec/ac3dec.h b/libavcodec/ac3dec.h
> index 38c2deb..79ed731 100644
> --- a/libavcodec/ac3dec.h
> +++ b/libavcodec/ac3dec.h
> @@ -42,6 +42,7 @@
> #define AC3_MAX_COEFS 256
> #define AC3_BLOCK_SIZE 256
> #define MAX_BLOCKS 6
> +#define SPX_MAX_BANDS 17
>
> typedef struct {
> AVCodecContext *avctx; ///< parent context
> @@ -88,6 +89,23 @@ typedef struct {
> int cpl_coords[AC3_MAX_CHANNELS][18]; ///< coupling coordinates (cplco)
> ///@}
>
> +///@defgroup spx spectral extension
> +///@{
> + int spx_in_use; ///< spectral extension in use (spxinu)
> + uint8_t channel_in_spx[AC3_MAX_CHANNELS]; ///< channel in spectral extension (chinspx)
channel uses spectral extension ?
> + int8_t spx_atten_code[AC3_MAX_CHANNELS]; ///< spx attenuation code (spxattencod)
> + int spx_start_subband; ///< spx beginning frequency band (spxbegf)
> + int spx_start_freq; ///< spx start frequency bin
> + int spx_end_freq; ///< spx end frequency bin
what are frequency bins?
> + int spx_copy_start_freq; ///< spx starting frequency for copying (copystartmant)
frequency in hz ?
> + int num_spx_bands; ///< number of spx bands (nspxbnds)
> + uint8_t spx_band_struct[SPX_MAX_BANDS]; ///< spectral extension band structure (spxbndstrc)
what is a spectral extension band structure?
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
No great genius has ever existed without some touch of madness. -- Aristotle
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