shithub: opus

Info  •  Files  •  Log  •  Branches

Improving CBR for hybrid mode

Hybrid CBR now simply forces the SILK CBR rate to the "target" value. Also,
we're getting rid of the -2 kb/s offset for CBR, which appeared to be harmful.
In the case of hybrid constrained VBR, the cap is computed in the same way
as the target.

--- a/src/opus_encoder.c

+++ b/src/opus_encoder.c

@@ -1792,14 +1792,21 @@

         nBytes = IMIN(1275, max_data_bytes-1-redundancy_bytes);

         st->silk_mode.maxBits = nBytes*8;

-        /* Only allow up to 90% of the bits for hybrid mode*/

-        if (st->mode == MODE_HYBRID)

-           st->silk_mode.maxBits = (opus_int32)st->silk_mode.maxBits*9/10;

         if (st->silk_mode.useCBR)

         {

-           st->silk_mode.maxBits = (st->silk_mode.bitRate * frame_size / (st->Fs * 8))*8;

-           /* Reduce the initial target to make it easier to reach the CBR rate */

-           st->silk_mode.bitRate = IMAX(1, st->silk_mode.bitRate-2000);

+           if (st->mode == MODE_HYBRID)

+           {

+              st->silk_mode.maxBits = st->silk_mode.bitRate * frame_size / st->Fs;

+           }

+        } else {

+           /* Constrained VBR. */

+           if (st->mode == MODE_HYBRID)

+           {

+              /* Compute SILK bitrate corresponding to the max total bits available */

+              opus_int32 maxBitRate = compute_silk_rate_for_hybrid(nBytes*8*st->Fs / frame_size,

+                    curr_bandwidth, st->Fs == 50 * frame_size, st->use_vbr);

+              st->silk_mode.maxBits = maxBitRate * frame_size / st->Fs;

+           }

         }

         if (prefill)