eac3enc: use different numbers of blocks per frame to allow higher bitrates

6 files changed, 142 insertions, 97 deletions

diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
index e7a5b1611e..017b1d4b93 100644
--- a/libavcodec/ac3enc.c
+++ b/libavcodec/ac3enc.c
@@ -186,7 +186,7 @@ void ff_ac3_adjust_frame_size(AC3EncodeContext *s)
     s->frame_size = s->frame_size_min +
                     2 * (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
     s->bits_written    += s->frame_size * 8;
-    s->samples_written += AC3_FRAME_SIZE;
+    s->samples_written += AC3_BLOCK_SIZE * s->num_blocks;
 }
 
 
@@ -198,7 +198,7 @@ void ff_ac3_compute_coupling_strategy(AC3EncodeContext *s)
 
     /* set coupling use flags for each block/channel */
     /* TODO: turn coupling on/off and adjust start band based on bit usage */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         for (ch = 1; ch <= s->fbw_channels; ch++)
             block->channel_in_cpl[ch] = s->cpl_on;
@@ -208,7 +208,7 @@ void ff_ac3_compute_coupling_strategy(AC3EncodeContext *s)
        enabled for that block */
     got_cpl_snr = 0;
     num_cpl_blocks = 0;
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         block->num_cpl_channels = 0;
         for (ch = 1; ch <= s->fbw_channels; ch++)
@@ -244,7 +244,7 @@ void ff_ac3_compute_coupling_strategy(AC3EncodeContext *s)
         s->cpl_on = 0;
 
     /* set bandwidth for each channel */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         for (ch = 1; ch <= s->fbw_channels; ch++) {
             if (block->channel_in_cpl[ch])
@@ -269,7 +269,7 @@ void ff_ac3_apply_rematrixing(AC3EncodeContext *s)
     if (!s->rematrixing_enabled)
         return;
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         if (block->new_rematrixing_strategy)
             flags = block->rematrixing_flags;
@@ -318,7 +318,7 @@ static av_cold void exponent_init(AC3EncodeContext *s)
 static void extract_exponents(AC3EncodeContext *s)
 {
     int ch        = !s->cpl_on;
-    int chan_size = AC3_MAX_COEFS * AC3_MAX_BLOCKS * (s->channels - ch + 1);
+    int chan_size = AC3_MAX_COEFS * s->num_blocks * (s->channels - ch + 1);
     AC3Block *block = &s->blocks[0];
 
     s->ac3dsp.extract_exponents(block->exp[ch], block->fixed_coef[ch], chan_size);
@@ -331,6 +331,15 @@ static void extract_exponents(AC3EncodeContext *s)
  */
 #define EXP_DIFF_THRESHOLD 500
 
+/**
+ * Table used to select exponent strategy based on exponent reuse block interval.
+ */
+static const uint8_t exp_strategy_reuse_tab[4][6] = {
+    { EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
+    { EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
+    { EXP_D25, EXP_D25, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
+    { EXP_D45, EXP_D25, EXP_D25, EXP_D15, EXP_D15, EXP_D15 }
+};
 
 /**
  * Calculate exponent strategies for all channels.
@@ -349,7 +358,7 @@ static void compute_exp_strategy(AC3EncodeContext *s)
            reused in the next frame */
         exp_strategy[0] = EXP_NEW;
         exp += AC3_MAX_COEFS;
-        for (blk = 1; blk < AC3_MAX_BLOCKS; blk++, exp += AC3_MAX_COEFS) {
+        for (blk = 1; blk < s->num_blocks; blk++, exp += AC3_MAX_COEFS) {
             if (ch == CPL_CH) {
                 if (!s->blocks[blk-1].cpl_in_use) {
                     exp_strategy[blk] = EXP_NEW;
@@ -373,23 +382,18 @@ static void compute_exp_strategy(AC3EncodeContext *s)
         /* now select the encoding strategy type : if exponents are often
            recoded, we use a coarse encoding */
         blk = 0;
-        while (blk < AC3_MAX_BLOCKS) {
+        while (blk < s->num_blocks) {
             blk1 = blk + 1;
-            while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE)
+            while (blk1 < s->num_blocks && exp_strategy[blk1] == EXP_REUSE)
                 blk1++;
-            switch (blk1 - blk) {
-            case 1:  exp_strategy[blk] = EXP_D45; break;
-            case 2:
-            case 3:  exp_strategy[blk] = EXP_D25; break;
-            default: exp_strategy[blk] = EXP_D15; break;
-            }
+            exp_strategy[blk] = exp_strategy_reuse_tab[s->num_blks_code][blk1-blk-1];
             blk = blk1;
         }
     }
     if (s->lfe_on) {
         ch = s->lfe_channel;
         s->exp_strategy[ch][0] = EXP_D15;
-        for (blk = 1; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 1; blk < s->num_blocks; blk++)
             s->exp_strategy[ch][blk] = EXP_REUSE;
     }
 
@@ -487,7 +491,7 @@ static void encode_exponents(AC3EncodeContext *s)
 
         cpl = (ch == CPL_CH);
         blk = 0;
-        while (blk < AC3_MAX_BLOCKS) {
+        while (blk < s->num_blocks) {
             AC3Block *block = &s->blocks[blk];
             if (cpl && !block->cpl_in_use) {
                 exp += AC3_MAX_COEFS;
@@ -500,7 +504,7 @@ static void encode_exponents(AC3EncodeContext *s)
             /* count the number of EXP_REUSE blocks after the current block
                and set exponent reference block numbers */
             s->exp_ref_block[ch][blk] = blk;
-            while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE) {
+            while (blk1 < s->num_blocks && exp_strategy[blk1] == EXP_REUSE) {
                 s->exp_ref_block[ch][blk1] = blk;
                 blk1++;
             }
@@ -536,7 +540,7 @@ static void group_exponents(AC3EncodeContext *s)
     int exp0, exp1;
 
     bit_count = 0;
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         for (ch = !block->cpl_in_use; ch <= s->channels; ch++) {
             int exp_strategy = s->exp_strategy[ch][blk];
@@ -625,30 +629,38 @@ static void count_frame_bits_fixed(AC3EncodeContext *s)
     if (s->eac3) {
         /* bitstream info header */
         frame_bits += 35;
-        frame_bits += 1 + 1 + 1;
+        frame_bits += 1 + 1;
+        if (s->num_blocks != 0x6)
+            frame_bits++;
+        frame_bits++;
         /* audio frame header */
-        frame_bits += 2;
+        if (s->num_blocks == 6)
+            frame_bits += 2;
         frame_bits += 10;
         /* exponent strategy */
         if (s->use_frame_exp_strategy)
             frame_bits += 5 * s->fbw_channels;
         else
-            frame_bits += AC3_MAX_BLOCKS * 2 * s->fbw_channels;
+            frame_bits += s->num_blocks * 2 * s->fbw_channels;
         if (s->lfe_on)
-            frame_bits += AC3_MAX_BLOCKS;
+            frame_bits += s->num_blocks;
         /* converter exponent strategy */
-        frame_bits += s->fbw_channels * 5;
+        if (s->num_blks_code != 0x3)
+            frame_bits++;
+        else
+            frame_bits += s->fbw_channels * 5;
         /* snr offsets */
         frame_bits += 10;
         /* block start info */
-        frame_bits++;
+        if (s->num_blocks != 1)
+            frame_bits++;
     } else {
         frame_bits += 49;
         frame_bits += frame_bits_inc[s->channel_mode];
     }
 
     /* audio blocks */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         if (!s->eac3) {
             /* block switch flags */
             frame_bits += s->fbw_channels;
@@ -750,7 +762,7 @@ static void count_frame_bits(AC3EncodeContext *s)
         /* coupling */
         if (s->channel_mode > AC3_CHMODE_MONO) {
             frame_bits++;
-            for (blk = 1; blk < AC3_MAX_BLOCKS; blk++) {
+            for (blk = 1; blk < s->num_blocks; blk++) {
                 AC3Block *block = &s->blocks[blk];
                 frame_bits++;
                 if (block->new_cpl_strategy)
@@ -762,7 +774,7 @@ static void count_frame_bits(AC3EncodeContext *s)
             if (s->use_frame_exp_strategy) {
                 frame_bits += 5 * s->cpl_on;
             } else {
-                for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+                for (blk = 0; blk < s->num_blocks; blk++)
                     frame_bits += 2 * s->blocks[blk].cpl_in_use;
             }
         }
@@ -778,7 +790,7 @@ static void count_frame_bits(AC3EncodeContext *s)
     }
 
     /* audio blocks */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
 
         /* coupling strategy */
@@ -865,7 +877,7 @@ static void bit_alloc_masking(AC3EncodeContext *s)
 {
     int blk, ch;
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         for (ch = !block->cpl_in_use; ch <= s->channels; ch++) {
             /* We only need psd and mask for calculating bap.
@@ -901,9 +913,9 @@ static void reset_block_bap(AC3EncodeContext *s)
 
     ref_bap = s->bap_buffer;
     for (ch = 0; ch <= s->channels; ch++) {
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 0; blk < s->num_blocks; blk++)
             s->ref_bap[ch][blk] = ref_bap + AC3_MAX_COEFS * s->exp_ref_block[ch][blk];
-        ref_bap += AC3_MAX_COEFS * AC3_MAX_BLOCKS;
+        ref_bap += AC3_MAX_COEFS * s->num_blocks;
     }
     s->ref_bap_set = 1;
 }
@@ -936,7 +948,7 @@ static void count_mantissa_bits_update_ch(AC3EncodeContext *s, int ch,
 {
     int blk;
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         if (ch == CPL_CH && !block->cpl_in_use)
             continue;
@@ -980,7 +992,7 @@ static int bit_alloc(AC3EncodeContext *s, int snr_offset)
     snr_offset = (snr_offset - 240) << 2;
 
     reset_block_bap(s);
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
 
         for (ch = !block->cpl_in_use; ch <= s->channels; ch++) {
@@ -1194,7 +1206,7 @@ void ff_ac3_quantize_mantissas(AC3EncodeContext *s)
 {
     int blk, ch, ch0=0, got_cpl;
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         AC3Mant m = { 0 };
 
@@ -1557,7 +1569,7 @@ void ff_ac3_output_frame(AC3EncodeContext *s, unsigned char *frame)
 
     s->output_frame_header(s);
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+    for (blk = 0; blk < s->num_blocks; blk++)
         output_audio_block(s, blk);
 
     output_frame_end(s);
@@ -1585,6 +1597,7 @@ static void dprint_options(AC3EncodeContext *s)
     av_dlog(avctx, "channel_layout: %s\n", strbuf);
     av_dlog(avctx, "sample_rate: %d\n", s->sample_rate);
     av_dlog(avctx, "bit_rate: %d\n", s->bit_rate);
+    av_dlog(avctx, "blocks/frame: %d (code=%d)\n", s->num_blocks, s->num_blks_code);
     if (s->cutoff)
         av_dlog(avctx, "cutoff: %d\n", s->cutoff);
 
@@ -1851,7 +1864,7 @@ av_cold int ff_ac3_encode_close(AVCodecContext *avctx)
     av_freep(&s->qmant_buffer);
     av_freep(&s->cpl_coord_exp_buffer);
     av_freep(&s->cpl_coord_mant_buffer);
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         av_freep(&block->mdct_coef);
         av_freep(&block->fixed_coef);
@@ -1958,18 +1971,30 @@ static av_cold int validate_options(AC3EncodeContext *s)
     /* validate bit rate */
     if (s->eac3) {
         int max_br, min_br, wpf, min_br_dist, min_br_code;
+        int num_blks_code, num_blocks, frame_samples;
 
         /* calculate min/max bitrate */
-        max_br = 2048 * s->sample_rate / AC3_FRAME_SIZE * 16;
-        min_br = ((s->sample_rate + (AC3_FRAME_SIZE-1)) / AC3_FRAME_SIZE) * 16;
+        /* TODO: More testing with 3 and 2 blocks. All E-AC-3 samples I've
+                 found use either 6 blocks or 1 block, even though 2 or 3 blocks
+                 would work as far as the bit rate is concerned. */
+        for (num_blks_code = 3; num_blks_code >= 0; num_blks_code--) {
+            num_blocks = ((int[]){ 1, 2, 3, 6 })[num_blks_code];
+            frame_samples  = AC3_BLOCK_SIZE * num_blocks;
+            max_br = 2048 * s->sample_rate / frame_samples * 16;
+            min_br = ((s->sample_rate + (frame_samples-1)) / frame_samples) * 16;
+            if (avctx->bit_rate <= max_br)
+                break;
+        }
         if (avctx->bit_rate < min_br || avctx->bit_rate > max_br) {
             av_log(avctx, AV_LOG_ERROR, "invalid bit rate. must be %d to %d "
                    "for this sample rate\n", min_br, max_br);
             return AVERROR(EINVAL);
         }
+        s->num_blks_code = num_blks_code;
+        s->num_blocks    = num_blocks;
 
         /* calculate words-per-frame for the selected bitrate */
-        wpf = (avctx->bit_rate / 16) * AC3_FRAME_SIZE / s->sample_rate;
+        wpf = (avctx->bit_rate / 16) * frame_samples / s->sample_rate;
         av_assert1(wpf > 0 && wpf <= 2048);
 
         /* find the closest AC-3 bitrate code to the selected bitrate.
@@ -2001,6 +2026,8 @@ static av_cold int validate_options(AC3EncodeContext *s)
         }
         s->frame_size_code = i << 1;
         s->frame_size_min  = 2 * ff_ac3_frame_size_tab[s->frame_size_code][s->bit_alloc.sr_code];
+        s->num_blks_code   = 0x3;
+        s->num_blocks      = 6;
     }
     s->bit_rate   = avctx->bit_rate;
     s->frame_size = s->frame_size_min;
@@ -2065,13 +2092,13 @@ static av_cold void set_bandwidth(AC3EncodeContext *s)
     /* set number of coefficients for each channel */
     for (ch = 1; ch <= s->fbw_channels; ch++) {
         s->start_freq[ch] = 0;
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 0; blk < s->num_blocks; blk++)
             s->blocks[blk].end_freq[ch] = s->bandwidth_code * 3 + 73;
     }
     /* LFE channel always has 7 coefs */
     if (s->lfe_on) {
         s->start_freq[s->lfe_channel] = 0;
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 0; blk < s->num_blocks; blk++)
             s->blocks[blk].end_freq[ch] = 7;
     }
 
@@ -2108,7 +2135,7 @@ static av_cold void set_bandwidth(AC3EncodeContext *s)
 
         s->start_freq[CPL_CH] = cpl_start_band * 12 + 37;
         s->cpl_end_freq       = cpl_end_band   * 12 + 37;
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 0; blk < s->num_blocks; blk++)
             s->blocks[blk].end_freq[CPL_CH] = s->cpl_end_freq;
     }
 }
@@ -2119,35 +2146,37 @@ static av_cold int allocate_buffers(AC3EncodeContext *s)
     AVCodecContext *avctx = s->avctx;
     int blk, ch;
     int channels = s->channels + 1; /* includes coupling channel */
+    int channel_blocks = channels * s->num_blocks;
+    int total_coefs    = AC3_MAX_COEFS * channel_blocks;
 
     if (s->allocate_sample_buffers(s))
         goto alloc_fail;
 
-    FF_ALLOC_OR_GOTO(avctx, s->bap_buffer,  AC3_MAX_BLOCKS * channels *
-                     AC3_MAX_COEFS * sizeof(*s->bap_buffer),  alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->bap1_buffer, AC3_MAX_BLOCKS * channels *
-                     AC3_MAX_COEFS * sizeof(*s->bap1_buffer), alloc_fail);
-    FF_ALLOCZ_OR_GOTO(avctx, s->mdct_coef_buffer, AC3_MAX_BLOCKS * channels *
-                      AC3_MAX_COEFS * sizeof(*s->mdct_coef_buffer), alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->exp_buffer, AC3_MAX_BLOCKS * channels *
-                     AC3_MAX_COEFS * sizeof(*s->exp_buffer), alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->grouped_exp_buffer, AC3_MAX_BLOCKS * channels *
-                     128 * sizeof(*s->grouped_exp_buffer), alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->psd_buffer, AC3_MAX_BLOCKS * channels *
-                     AC3_MAX_COEFS * sizeof(*s->psd_buffer), alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->band_psd_buffer, AC3_MAX_BLOCKS * channels *
-                     64 * sizeof(*s->band_psd_buffer), alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->mask_buffer, AC3_MAX_BLOCKS * channels *
-                     64 * sizeof(*s->mask_buffer), alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, s->qmant_buffer, AC3_MAX_BLOCKS * channels *
-                     AC3_MAX_COEFS * sizeof(*s->qmant_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->bap_buffer, total_coefs *
+                     sizeof(*s->bap_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->bap1_buffer, total_coefs *
+                     sizeof(*s->bap1_buffer), alloc_fail);
+    FF_ALLOCZ_OR_GOTO(avctx, s->mdct_coef_buffer, total_coefs *
+                      sizeof(*s->mdct_coef_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->exp_buffer, total_coefs *
+                     sizeof(*s->exp_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->grouped_exp_buffer, channel_blocks * 128 *
+                     sizeof(*s->grouped_exp_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->psd_buffer, total_coefs *
+                     sizeof(*s->psd_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->band_psd_buffer, channel_blocks * 64 *
+                     sizeof(*s->band_psd_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->mask_buffer, channel_blocks * 64 *
+                     sizeof(*s->mask_buffer), alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, s->qmant_buffer, total_coefs *
+                     sizeof(*s->qmant_buffer), alloc_fail);
     if (s->cpl_enabled) {
-        FF_ALLOC_OR_GOTO(avctx, s->cpl_coord_exp_buffer, AC3_MAX_BLOCKS * channels *
-                         16 * sizeof(*s->cpl_coord_exp_buffer), alloc_fail);
-        FF_ALLOC_OR_GOTO(avctx, s->cpl_coord_mant_buffer, AC3_MAX_BLOCKS * channels *
-                         16 * sizeof(*s->cpl_coord_mant_buffer), alloc_fail);
+        FF_ALLOC_OR_GOTO(avctx, s->cpl_coord_exp_buffer, channel_blocks * 16 *
+                         sizeof(*s->cpl_coord_exp_buffer), alloc_fail);
+        FF_ALLOC_OR_GOTO(avctx, s->cpl_coord_mant_buffer, channel_blocks * 16 *
+                         sizeof(*s->cpl_coord_mant_buffer), alloc_fail);
     }
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         FF_ALLOCZ_OR_GOTO(avctx, block->mdct_coef, channels * sizeof(*block->mdct_coef),
                           alloc_fail);
@@ -2183,23 +2212,23 @@ static av_cold int allocate_buffers(AC3EncodeContext *s)
             }
 
             /* arrangement: channel, block, coeff */
-            block->exp[ch]         = &s->exp_buffer        [AC3_MAX_COEFS * (AC3_MAX_BLOCKS * ch + blk)];
-            block->mdct_coef[ch]   = &s->mdct_coef_buffer  [AC3_MAX_COEFS * (AC3_MAX_BLOCKS * ch + blk)];
+            block->exp[ch]         = &s->exp_buffer        [AC3_MAX_COEFS * (s->num_blocks * ch + blk)];
+            block->mdct_coef[ch]   = &s->mdct_coef_buffer  [AC3_MAX_COEFS * (s->num_blocks * ch + blk)];
         }
     }
 
     if (!s->fixed_point) {
-        FF_ALLOCZ_OR_GOTO(avctx, s->fixed_coef_buffer, AC3_MAX_BLOCKS * channels *
-                          AC3_MAX_COEFS * sizeof(*s->fixed_coef_buffer), alloc_fail);
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+        FF_ALLOCZ_OR_GOTO(avctx, s->fixed_coef_buffer, total_coefs *
+                          sizeof(*s->fixed_coef_buffer), alloc_fail);
+        for (blk = 0; blk < s->num_blocks; blk++) {
             AC3Block *block = &s->blocks[blk];
             FF_ALLOCZ_OR_GOTO(avctx, block->fixed_coef, channels *
                               sizeof(*block->fixed_coef), alloc_fail);
             for (ch = 0; ch < channels; ch++)
-                block->fixed_coef[ch] = &s->fixed_coef_buffer[AC3_MAX_COEFS * (AC3_MAX_BLOCKS * ch + blk)];
+                block->fixed_coef[ch] = &s->fixed_coef_buffer[AC3_MAX_COEFS * (s->num_blocks * ch + blk)];
         }
     } else {
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+        for (blk = 0; blk < s->num_blocks; blk++) {
             AC3Block *block = &s->blocks[blk];
             FF_ALLOCZ_OR_GOTO(avctx, block->fixed_coef, channels *
                               sizeof(*block->fixed_coef), alloc_fail);
@@ -2226,14 +2255,14 @@ av_cold int ff_ac3_encode_init(AVCodecContext *avctx)
 
     s->eac3 = avctx->codec_id == CODEC_ID_EAC3;
 
-    avctx->frame_size = AC3_FRAME_SIZE;
-
     ff_ac3_common_init();
 
     ret = validate_options(s);
     if (ret)
         return ret;
 
+    avctx->frame_size = AC3_BLOCK_SIZE * s->num_blocks;
+
     s->bitstream_mode = avctx->audio_service_type;
     if (s->bitstream_mode == AV_AUDIO_SERVICE_TYPE_KARAOKE)
         s->bitstream_mode = 0x7;
diff --git a/libavcodec/ac3enc.h b/libavcodec/ac3enc.h
index a4a8fd4325..407e751b40 100644
--- a/libavcodec/ac3enc.h
+++ b/libavcodec/ac3enc.h
@@ -151,6 +151,8 @@ typedef struct AC3EncodeContext {
     int bit_rate;                           ///< target bit rate, in bits-per-second
     int sample_rate;                        ///< sampling frequency, in Hz
 
+    int num_blks_code;                      ///< number of blocks code                  (numblkscod)
+    int num_blocks;                         ///< number of blocks per frame
     int frame_size_min;                     ///< minimum frame size in case rounding is necessary
     int frame_size;                         ///< current frame size in bytes
     int frame_size_code;                    ///< frame size code                        (frmsizecod)
diff --git a/libavcodec/ac3enc_fixed.c b/libavcodec/ac3enc_fixed.c
index ed8992ebff..508ecb1efb 100644
--- a/libavcodec/ac3enc_fixed.c
+++ b/libavcodec/ac3enc_fixed.c
@@ -93,7 +93,7 @@ static void scale_coefficients(AC3EncodeContext *s)
 {
     int blk, ch;
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         for (ch = 1; ch <= s->channels; ch++) {
             s->ac3dsp.ac3_rshift_int32(block->mdct_coef[ch], AC3_MAX_COEFS,
diff --git a/libavcodec/ac3enc_float.c b/libavcodec/ac3enc_float.c
index 776d185fa4..9f691a1e16 100644
--- a/libavcodec/ac3enc_float.c
+++ b/libavcodec/ac3enc_float.c
@@ -103,7 +103,7 @@ static int normalize_samples(AC3EncodeContext *s)
  */
 static void scale_coefficients(AC3EncodeContext *s)
 {
-    int chan_size = AC3_MAX_COEFS * AC3_MAX_BLOCKS;
+    int chan_size = AC3_MAX_COEFS * s->num_blocks;
     s->ac3dsp.float_to_fixed24(s->fixed_coef_buffer + chan_size,
                                s->mdct_coef_buffer  + chan_size,
                                chan_size * s->channels);
diff --git a/libavcodec/ac3enc_template.c b/libavcodec/ac3enc_template.c
index 9b9151b3e0..c4e2a121bf 100644
--- a/libavcodec/ac3enc_template.c
+++ b/libavcodec/ac3enc_template.c
@@ -79,13 +79,13 @@ static void deinterleave_input_samples(AC3EncodeContext *s,
         int sinc;
 
         /* copy last 256 samples of previous frame to the start of the current frame */
-        memcpy(&s->planar_samples[ch][0], &s->planar_samples[ch][AC3_FRAME_SIZE],
+        memcpy(&s->planar_samples[ch][0], &s->planar_samples[ch][AC3_BLOCK_SIZE * s->num_blocks],
                AC3_BLOCK_SIZE * sizeof(s->planar_samples[0][0]));
 
         /* deinterleave */
         sinc = s->channels;
         sptr = samples + s->channel_map[ch];
-        for (i = AC3_BLOCK_SIZE; i < AC3_FRAME_SIZE+AC3_BLOCK_SIZE; i++) {
+        for (i = AC3_BLOCK_SIZE; i < AC3_BLOCK_SIZE * (s->num_blocks + 1); i++) {
             s->planar_samples[ch][i] = *sptr;
             sptr += sinc;
         }
@@ -103,7 +103,7 @@ static void apply_mdct(AC3EncodeContext *s)
     int blk, ch;
 
     for (ch = 0; ch < s->channels; ch++) {
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+        for (blk = 0; blk < s->num_blocks; blk++) {
             AC3Block *block = &s->blocks[blk];
             const SampleType *input_samples = &s->planar_samples[ch][blk * AC3_BLOCK_SIZE];
 
@@ -159,7 +159,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
     cpl_start     = FFMIN(256, cpl_start + num_cpl_coefs) - num_cpl_coefs;
 
     /* calculate coupling channel from fbw channels */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         CoefType *cpl_coef = &block->mdct_coef[CPL_CH][cpl_start];
         if (!block->cpl_in_use)
@@ -188,7 +188,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
     while (i < s->cpl_end_freq) {
         int band_size = s->cpl_band_sizes[bnd];
         for (ch = CPL_CH; ch <= s->fbw_channels; ch++) {
-            for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+            for (blk = 0; blk < s->num_blocks; blk++) {
                 AC3Block *block = &s->blocks[blk];
                 if (!block->cpl_in_use || (ch > CPL_CH && !block->channel_in_cpl[ch]))
                     continue;
@@ -203,7 +203,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
     }
 
     /* determine which blocks to send new coupling coordinates for */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block  = &s->blocks[blk];
         AC3Block *block0 = blk ? &s->blocks[blk-1] : NULL;
         int new_coords = 0;
@@ -261,7 +261,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
        coordinates in successive blocks */
     for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
         blk = 0;
-        while (blk < AC3_MAX_BLOCKS) {
+        while (blk < s->num_blocks) {
             int blk1;
             CoefSumType energy_cpl;
             AC3Block *block  = &s->blocks[blk];
@@ -273,7 +273,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
 
             energy_cpl = energy[blk][CPL_CH][bnd];
             blk1 = blk+1;
-            while (!s->blocks[blk1].new_cpl_coords && blk1 < AC3_MAX_BLOCKS) {
+            while (!s->blocks[blk1].new_cpl_coords && blk1 < s->num_blocks) {
                 if (s->blocks[blk1].cpl_in_use)
                     energy_cpl += energy[blk1][CPL_CH][bnd];
                 blk1++;
@@ -285,7 +285,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
                     continue;
                 energy_ch = energy[blk][ch][bnd];
                 blk1 = blk+1;
-                while (!s->blocks[blk1].new_cpl_coords && blk1 < AC3_MAX_BLOCKS) {
+                while (!s->blocks[blk1].new_cpl_coords && blk1 < s->num_blocks) {
                     if (s->blocks[blk1].cpl_in_use)
                         energy_ch += energy[blk1][ch][bnd];
                     blk1++;
@@ -297,7 +297,7 @@ static void apply_channel_coupling(AC3EncodeContext *s)
     }
 
     /* calculate exponents/mantissas for coupling coordinates */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         if (!block->cpl_in_use || !block->new_cpl_coords)
             continue;
@@ -362,7 +362,7 @@ static void compute_rematrixing_strategy(AC3EncodeContext *s)
     if (s->channel_mode != AC3_CHMODE_STEREO)
         return;
 
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         block = &s->blocks[blk];
         block->new_rematrixing_strategy = !blk;
 
@@ -440,7 +440,7 @@ int AC3_NAME(encode_frame)(AVCodecContext *avctx, unsigned char *frame,
         scale_coefficients(s);
 
     clip_coefficients(&s->dsp, s->blocks[0].mdct_coef[1],
-                      AC3_MAX_COEFS * AC3_MAX_BLOCKS * s->channels);
+                      AC3_MAX_COEFS * s->num_blocks * s->channels);
 
     s->cpl_on = s->cpl_enabled;
     ff_ac3_compute_coupling_strategy(s);
diff --git a/libavcodec/eac3enc.c b/libavcodec/eac3enc.c
index 09fa80fcb9..038aa2a234 100644
--- a/libavcodec/eac3enc.c
+++ b/libavcodec/eac3enc.c
@@ -63,6 +63,11 @@ void ff_eac3_get_frame_exp_strategy(AC3EncodeContext *s)
 {
     int ch;
 
+    if (s->num_blocks < 6) {
+        s->use_frame_exp_strategy = 0;
+        return;
+    }
+
     s->use_frame_exp_strategy = 1;
     for (ch = !s->cpl_on; ch <= s->fbw_channels; ch++) {
         int expstr = eac3_frame_expstr_index_tab[s->exp_strategy[ch][0]-1]
@@ -89,7 +94,7 @@ void ff_eac3_set_cpl_states(AC3EncodeContext *s)
     /* set first cpl coords */
     for (ch = 1; ch <= s->fbw_channels; ch++)
         first_cpl_coords[ch] = 1;
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         for (ch = 1; ch <= s->fbw_channels; ch++) {
             if (block->channel_in_cpl[ch]) {
@@ -104,7 +109,7 @@ void ff_eac3_set_cpl_states(AC3EncodeContext *s)
     }
 
     /* set first cpl leak */
-    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+    for (blk = 0; blk < s->num_blocks; blk++) {
         AC3Block *block = &s->blocks[blk];
         if (block->cpl_in_use) {
             block->new_cpl_leak = 2;
@@ -130,7 +135,7 @@ void ff_eac3_output_frame_header(AC3EncodeContext *s)
         put_bits(&s->pb, 2, s->bit_alloc.sr_code);  /* sample rate code */
     } else {
         put_bits(&s->pb, 2, s->bit_alloc.sr_code);  /* sample rate code */
-        put_bits(&s->pb, 2, 0x3);                   /* number of blocks = 6 */
+        put_bits(&s->pb, 2, s->num_blks_code);      /* number of blocks */
     }
     put_bits(&s->pb, 3, s->channel_mode);           /* audio coding mode */
     put_bits(&s->pb, 1, s->lfe_on);                 /* LFE channel indicator */
@@ -141,11 +146,15 @@ void ff_eac3_output_frame_header(AC3EncodeContext *s)
     /* TODO: mixing metadata */
     put_bits(&s->pb, 1, 0);                         /* no info metadata */
     /* TODO: info metadata */
+    if (s->num_blocks != 6)
+        put_bits(&s->pb, 1, !(s->avctx->frame_number % 6)); /* converter sync flag */
     put_bits(&s->pb, 1, 0);                         /* no additional bit stream info */
 
     /* frame header */
+    if (s->num_blocks == 6) {
     put_bits(&s->pb, 1, !s->use_frame_exp_strategy);/* exponent strategy syntax */
     put_bits(&s->pb, 1, 0);                         /* aht enabled = no */
+    }
     put_bits(&s->pb, 2, 0);                         /* snr offset strategy = 1 */
     put_bits(&s->pb, 1, 0);                         /* transient pre-noise processing enabled = no */
     put_bits(&s->pb, 1, 0);                         /* block switch syntax enabled = no */
@@ -158,7 +167,7 @@ void ff_eac3_output_frame_header(AC3EncodeContext *s)
     /* coupling strategy use flags */
     if (s->channel_mode > AC3_CHMODE_MONO) {
         put_bits(&s->pb, 1, s->blocks[0].cpl_in_use);
-        for (blk = 1; blk < AC3_MAX_BLOCKS; blk++) {
+        for (blk = 1; blk < s->num_blocks; blk++) {
             AC3Block *block = &s->blocks[blk];
             put_bits(&s->pb, 1, block->new_cpl_strategy);
             if (block->new_cpl_strategy)
@@ -170,26 +179,31 @@ void ff_eac3_output_frame_header(AC3EncodeContext *s)
         for (ch = !s->cpl_on; ch <= s->fbw_channels; ch++)
             put_bits(&s->pb, 5, s->frame_exp_strategy[ch]);
     } else {
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 0; blk < s->num_blocks; blk++)
             for (ch = !s->blocks[blk].cpl_in_use; ch <= s->fbw_channels; ch++)
                 put_bits(&s->pb, 2, s->exp_strategy[ch][blk]);
     }
     if (s->lfe_on) {
-        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
+        for (blk = 0; blk < s->num_blocks; blk++)
             put_bits(&s->pb, 1, s->exp_strategy[s->lfe_channel][blk]);
     }
-    /* E-AC-3 to AC-3 converter exponent strategy (unfortunately not optional...) */
+    /* E-AC-3 to AC-3 converter exponent strategy (not optional when num blocks == 6) */
+    if (s->num_blocks != 6) {
+        put_bits(&s->pb, 1, 0);
+    } else {
     for (ch = 1; ch <= s->fbw_channels; ch++) {
         if (s->use_frame_exp_strategy)
             put_bits(&s->pb, 5, s->frame_exp_strategy[ch]);
         else
             put_bits(&s->pb, 5, 0);
     }
+    }
     /* snr offsets */
     put_bits(&s->pb, 6, s->coarse_snr_offset);
     put_bits(&s->pb, 4, s->fine_snr_offset[1]);
     /* block start info */
-    put_bits(&s->pb, 1, 0);
+    if (s->num_blocks > 1)
+        put_bits(&s->pb, 1, 0);
 }