@@ -1037,10 +1037,10 @@ static int residue_encode(vorbis_enc_context *venc, vorbis_enc_residue *rc,
* See Vorbis I spec Fig. 2, 3 for examples.
*/
static void apply_window(vorbis_enc_context *venc, const int *blockflags,
- float *out, float* in)
+ float *out, float* in, const float clip_factor)
{
int prev_size, curr_size, next_size, bound;
- float scale = 1.0f / (float) (1 << (venc->log2_blocksize[blockflags[1]] - 2));
+ float scale = clip_factor / (float) (1 << (venc->log2_blocksize[blockflags[1]] - 2));
const float *prev_win, *next_win;
AVFloatDSPContext *fdsp = venc->fdsp;
@@ -1098,9 +1098,9 @@ static int apply_window_and_mdct(vorbis_enc_context *venc, int next_type)
for (channel = 0; channel < venc->channels; channel++) {
float *out = venc->scratch;
float *in = venc->samples + channel * 2 * long_len + transient_offset;
+ float clip_factor = ff_psy_vorbis_avoid_clip(in, curr_len, curr_type);
- apply_window(venc, blockflags, out, in);
-
+ apply_window(venc, blockflags, out, in, clip_factor);
venc->mdct[curr_type].mdct_calc(&venc->mdct[curr_type],
venc->coeffs + channel * curr_len, out);
}
@@ -140,6 +140,23 @@ int ff_psy_vorbis_block_frame(VorbisPsyContext *vpctx, float *audio,
return block_flag;
}
+float ff_psy_vorbis_avoid_clip(float *audio, int window_len, int blockflag)
+{
+ int i;
+ float max = 0, clip = 1.0f;
+ /* Due to how the mdct scaling works in the vorbis encoder, short blocks are
+ * more likely to clip. This serves as more fine-grained control */
+ const float avoidance_factor = blockflag ? 0.95f : 0.75f;
+
+ for (i = 0; i < window_len; i++)
+ max = FFMAX(max, fabsf(audio[i]));
+
+ if (max > avoidance_factor)
+ clip = avoidance_factor / max;
+
+ return clip;
+}
+
av_cold void ff_psy_vorbis_close(VorbisPsyContext *vpctx)
{
av_freep(&vpctx->filter_delay);
@@ -75,6 +75,16 @@ av_cold int ff_psy_vorbis_init(VorbisPsyContext *vpctx, int sample_rate,
*/
int ff_psy_vorbis_block_frame(VorbisPsyContext *vpctx, float *audio,
int ch, int frame_size, int block_size);
+
+/**
+ * Provide a scalar coefficient to avoid clipping.
+ *
+ * @param audio Raw audio sample input for one channel
+ * @param window_len Chosen window length for the given frame
+ * @return Coefficient to be applied alongside the window function
+ */
+float ff_psy_vorbis_avoid_clip(float *audio, int window_len, int blockflag);
+
/**
* Closes and frees the memory used by the psychoacoustic model
*/
Clipping is avoided by taking the maximum value of each frame before window application, and scaling down the entire frame by a scalar factor. Signed-off-by: Tyler Jones <tdjones879@gmail.com> --- libavcodec/vorbisenc.c | 8 ++++---- libavcodec/vorbispsy.c | 17 +++++++++++++++++ libavcodec/vorbispsy.h | 10 ++++++++++ 3 files changed, 31 insertions(+), 4 deletions(-)