[FFmpeg-devel] [PATCH] avcodec/mlpdec: parse and use substream_info bits

[Paul B Mahol <onemda@gmail.com>]

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Patch attached.

Fixes relative recent thd regression.

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From 1715a7f4b0487c9ecebfedfc796377022a85baec Mon Sep 17 00:00:00 2001
From: Paul B Mahol <onemda@gmail.com>
Date: Mon, 30 Jan 2023 19:35:36 +0100
Subject: [PATCH] avcodec/mlpdec: parse and use substream info bits

Signed-off-by: Paul B Mahol <onemda@gmail.com>
---
 libavcodec/mlp_parse.c |  6 +++++-
 libavcodec/mlp_parse.h |  3 +++
 libavcodec/mlpdec.c    | 15 ++++++++++++++-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/libavcodec/mlp_parse.c b/libavcodec/mlp_parse.c
index 45715352c2..924c731439 100644
--- a/libavcodec/mlp_parse.c
+++ b/libavcodec/mlp_parse.c
@@ -159,7 +159,11 @@ int ff_mlp_read_major_sync(void *log, MLPHeaderInfo *mh, GetBitContext *gb)
 
     mh->num_substreams = get_bits(gb, 4);
 
-    skip_bits_long(gb, 4 + (header_size - 17) * 8);
+    skip_bits(gb, 2);
+    mh->extended_substream_info = get_bits(gb, 2);
+    mh->substream_info = get_bits(gb, 8);
+
+    skip_bits_long(gb, (header_size - 18) * 8);
 
     return 0;
 }
diff --git a/libavcodec/mlp_parse.h b/libavcodec/mlp_parse.h
index f0d7b41c11..fa6e3d52dc 100644
--- a/libavcodec/mlp_parse.h
+++ b/libavcodec/mlp_parse.h
@@ -58,6 +58,9 @@ typedef struct MLPHeaderInfo
     int peak_bitrate;                       ///< Peak bitrate for VBR, actual bitrate (==peak) for CBR
 
     int num_substreams;                     ///< Number of substreams within stream
+
+    int extended_substream_info;            ///< Which substream of substreams carry 16-channel presentation
+    int substream_info;                     ///< Which substream of substreams carry 2/6/8-channel presentation
 } MLPHeaderInfo;
 
 static const uint8_t thd_chancount[13] = {
diff --git a/libavcodec/mlpdec.c b/libavcodec/mlpdec.c
index 5b14a3b03b..c7b2ca21a1 100644
--- a/libavcodec/mlpdec.c
+++ b/libavcodec/mlpdec.c
@@ -153,6 +153,12 @@ typedef struct MLPDecodeContext {
     /// Number of substreams contained within this stream.
     uint8_t     num_substreams;
 
+    ///< Which substream of substreams carry 16-channel presentation
+    uint8_t     extended_substream_info;
+
+    ///< Which substream of substreams carry 2/6/8-channel presentation
+    uint8_t     substream_info;
+
     /// Index of the last substream to decode - further substreams are skipped.
     uint8_t     max_decoded_substream;
 
@@ -384,6 +390,7 @@ static int read_major_sync(MLPDecodeContext *m, GetBitContext *gb)
     m->access_unit_size_pow2 = mh.access_unit_size_pow2;
 
     m->num_substreams        = mh.num_substreams;
+    m->substream_info        = mh.substream_info;
 
     /* limit to decoding 3 substreams, as the 4th is used by Dolby Atmos for non-audio data */
     m->max_decoded_substream = FFMIN(m->num_substreams - 1, 2);
@@ -1286,7 +1293,13 @@ static int read_access_unit(AVCodecContext *avctx, AVFrame *frame,
             if (!s->restart_seen)
                 goto next_substr;
 
-            if (substr > 0 && substr < m->max_decoded_substream &&
+            if (((avctx->ch_layout.nb_channels == 6 &&
+                  ((m->substream_info >> 2) & 0x3) != 0x3) ||
+                 (avctx->ch_layout.nb_channels == 8 &&
+                  ((m->substream_info >> 4) & 0x7) != 0x7 &&
+                  ((m->substream_info >> 4) & 0x7) != 0x6 &&
+                  ((m->substream_info >> 4) & 0x7) != 0x3)) &&
+                substr > 0 && substr < m->max_decoded_substream &&
                 (s->min_channel <= m->substream[substr - 1].max_channel)) {
                 av_log(avctx, AV_LOG_DEBUG,
                        "Previous substream(%d) channels overlaps current substream(%d) channels, skipping.\n",
-- 
2.39.1


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