From 30cac8313aa80ad175c001a4773d3ce61c65d982 Mon Sep 17 00:00:00 2001
From: Christophe Gisquet <christophe.gisquet@gmail.com>
Date: Mon, 18 Aug 2014 09:53:20 +0200
Subject: alac: add option to decoded incorrect ALAC

Prior to 56.1.100, incorrect ALAC files for 24bps content were produced, in
particular not decoding losslessly.

Add an option to allow correctly decoding those streams.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
---
 libavcodec/alac.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

(limited to 'libavcodec/alac.c')

diff --git a/libavcodec/alac.c b/libavcodec/alac.c
index 103d14eada..aec7bb4e4e 100644
--- a/libavcodec/alac.c
+++ b/libavcodec/alac.c
@@ -48,6 +48,7 @@
 #include <inttypes.h>
 
 #include "libavutil/channel_layout.h"
+#include "libavutil/opt.h"
 #include "avcodec.h"
 #include "get_bits.h"
 #include "bytestream.h"
@@ -60,6 +61,7 @@
 #define ALAC_EXTRADATA_SIZE 36
 
 typedef struct {
+    AVClass *class;
     AVCodecContext *avctx;
     GetBitContext gb;
     int channels;
@@ -78,6 +80,7 @@ typedef struct {
     int nb_samples;     /**< number of samples in the current frame */
 
     int direct_output;
+    int extra_bit_bug;
 } ALACContext;
 
 static inline unsigned int decode_scalar(GetBitContext *gb, int k, int bps)
@@ -380,12 +383,17 @@ static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
         decorr_left_weight = 0;
     }
 
+    if (alac->extra_bits && alac->extra_bit_bug) {
+        append_extra_bits(alac->output_samples_buffer, alac->extra_bits_buffer,
+                          alac->extra_bits, channels, alac->nb_samples);
+    }
+
     if (channels == 2 && decorr_left_weight) {
         decorrelate_stereo(alac->output_samples_buffer, alac->nb_samples,
                            decorr_shift, decorr_left_weight);
     }
 
-    if (alac->extra_bits) {
+    if (alac->extra_bits && !alac->extra_bit_bug) {
         append_extra_bits(alac->output_samples_buffer, alac->extra_bits_buffer,
                           alac->extra_bits, channels, alac->nb_samples);
     }
@@ -630,6 +638,20 @@ static int init_thread_copy(AVCodecContext *avctx)
     return allocate_buffers(alac);
 }
 
+static const AVOption options[] = {
+    { "extra_bits_bug", "Force non-standard decoding process",
+      offsetof(ALACContext, extra_bit_bug), AV_OPT_TYPE_INT, { .i64 = 0 },
+      0, 1, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_DECODING_PARAM },
+    { NULL },
+};
+
+static const AVClass alac_class = {
+    .class_name = "alac",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
 AVCodec ff_alac_decoder = {
     .name           = "alac",
     .long_name      = NULL_IF_CONFIG_SMALL("ALAC (Apple Lossless Audio Codec)"),
@@ -641,4 +663,5 @@ AVCodec ff_alac_decoder = {
     .decode         = alac_decode_frame,
     .init_thread_copy = ONLY_IF_THREADS_ENABLED(init_thread_copy),
     .capabilities   = CODEC_CAP_DR1 | CODEC_CAP_FRAME_THREADS,
+    .priv_class     = &alac_class
 };
-- 
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