Block usage of frames with only constant subframes

Quite a lot of decoders have trouble streaming or seeking in a
file with frames that only consist of constant subframes because
of the large difference between the largest and smallest subframe.
To remedy this, this commit makes disables the use of constant
subframes for the last subframe in case all others are constant

src/libFLAC/fixed.c

@@ -235,13 +235,14 @@ uint32_t FLAC__fixed_compute_best_predictor(const FLAC__int32 data[], uint32_t d
 		error -= last_error_3; total_error_4 += local_abs(error); last_error_3 = save;
 	}
 
-	if(total_error_0 < flac_min(flac_min(flac_min(total_error_1, total_error_2), total_error_3), total_error_4))
+	/* prefer lower order */
+	if(total_error_0 <= flac_min(flac_min(flac_min(total_error_1, total_error_2), total_error_3), total_error_4))
 		order = 0;
-	else if(total_error_1 < flac_min(flac_min(total_error_2, total_error_3), total_error_4))
+	else if(total_error_1 <= flac_min(flac_min(total_error_2, total_error_3), total_error_4))
 		order = 1;
-	else if(total_error_2 < flac_min(total_error_3, total_error_4))
+	else if(total_error_2 <= flac_min(total_error_3, total_error_4))
 		order = 2;
-	else if(total_error_3 < total_error_4)
+	else if(total_error_3 <= total_error_4)
 		order = 3;
 	else
 		order = 4;

src/libFLAC/fixed_intrin_sse2.c

@@ -121,14 +121,14 @@ uint32_t FLAC__fixed_compute_best_predictor_intrin_sse2(const FLAC__int32 data[]
 	total_error_3 = _mm_cvtsi128_si32(total_err2);
 	total_error_1 = _mm_cvtsi128_si32(total_err1);
 
-	/* prefer higher order */
-	if(total_error_0 < flac_min(flac_min(flac_min(total_error_1, total_error_2), total_error_3), total_error_4))
+	/* prefer lower order */
+	if(total_error_0 <= flac_min(flac_min(flac_min(total_error_1, total_error_2), total_error_3), total_error_4))
 		order = 0;
-	else if(total_error_1 < flac_min(flac_min(total_error_2, total_error_3), total_error_4))
+	else if(total_error_1 <= flac_min(flac_min(total_error_2, total_error_3), total_error_4))
 		order = 1;
-	else if(total_error_2 < flac_min(total_error_3, total_error_4))
+	else if(total_error_2 <= flac_min(total_error_3, total_error_4))
 		order = 2;
-	else if(total_error_3 < total_error_4)
+	else if(total_error_3 <= total_error_4)
 		order = 3;
 	else
 		order = 4;

src/libFLAC/fixed_intrin_ssse3.c

@@ -115,14 +115,14 @@ uint32_t FLAC__fixed_compute_best_predictor_intrin_ssse3(const FLAC__int32 data[
 	total_error_3 = _mm_cvtsi128_si32(total_err2);
 	total_error_1 = _mm_cvtsi128_si32(total_err1);
 
-	/* prefer higher order */
-	if(total_error_0 < flac_min(flac_min(flac_min(total_error_1, total_error_2), total_error_3), total_error_4))
+	/* prefer lower order */
+	if(total_error_0 <= flac_min(flac_min(flac_min(total_error_1, total_error_2), total_error_3), total_error_4))
 		order = 0;
-	else if(total_error_1 < flac_min(flac_min(total_error_2, total_error_3), total_error_4))
+	else if(total_error_1 <= flac_min(flac_min(total_error_2, total_error_3), total_error_4))
 		order = 1;
-	else if(total_error_2 < flac_min(total_error_3, total_error_4))
+	else if(total_error_2 <= flac_min(total_error_3, total_error_4))
 		order = 2;
-	else if(total_error_3 < total_error_4)
+	else if(total_error_3 <= total_error_4)
 		order = 3;
 	else
 		order = 4;

src/libFLAC/stream_encoder.c

@@ -3140,7 +3140,7 @@ FLAC__bool process_subframes_(FLAC__StreamEncoder *encoder, FLAC__bool is_fracti
 {
 	FLAC__FrameHeader frame_header;
 	uint32_t channel, min_partition_order = encoder->protected_->min_residual_partition_order, max_partition_order;
-	FLAC__bool do_independent, do_mid_side;
+	FLAC__bool do_independent, do_mid_side, backup_disable_constant_subframes = encoder->private_->disable_constant_subframes, all_subframes_constant = true;
 
 	/*
 	 * Calculate the min,max Rice partition orders
@@ -3221,6 +3221,14 @@ FLAC__bool process_subframes_(FLAC__StreamEncoder *encoder, FLAC__bool is_fracti
 	 */
 	if(do_independent) {
 		for(channel = 0; channel < encoder->protected_->channels; channel++) {
+			if((channel + 1) == encoder->protected_->channels && all_subframes_constant){
+				/* This frame contains only constant subframes at this point. If the last subframe
+				 * is also constant, this will result in a very small frame. Quite a lot of decoders
+				 * have trouble streaming or seeking in a file which such small frames because of the
+				 * large difference between the largest and smallest subframe. To remedy this
+				 * further use of constant subframes in this frame will be disabled */
+				encoder->private_->disable_constant_subframes = true;
+			}
 			if(!
 				process_subframe_(
 					encoder,
@@ -3237,6 +3245,8 @@ FLAC__bool process_subframes_(FLAC__StreamEncoder *encoder, FLAC__bool is_fracti
 				)
 			)
 				return false;
+			if(&encoder->private_->subframe_workspace[channel][encoder->private_->best_subframe[channel]].type != FLAC__SUBFRAME_TYPE_CONSTANT)
+				all_subframes_constant = false;
 		}
 	}
 
@@ -3382,6 +3392,7 @@ FLAC__bool process_subframes_(FLAC__StreamEncoder *encoder, FLAC__bool is_fracti
 	}
 
 	encoder->private_->last_channel_assignment = frame_header.channel_assignment;
+	encoder->private_->disable_constant_subframes = backup_disable_constant_subframes;
 
 	return true;
 }

test/metaflac-test-files/case01-expect.meta

@@ -1,8 +1,8 @@
 a042237c5493fdb9656b94a83608d11a
 1152
 1152
-10
-10
+139
+155
 8000
 1
 8