[FFmpeg-devel] [PATCH] avcodec/mpegaudiodec_template: Don't modify AVCodecContext.priv_data (PR #20431)

[mkver via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20431 opened by mkver
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20431
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20431.patch


>From fcfe42e86c7c3027b80f60dd0a43a99ebedbdccb Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Thu, 4 Sep 2025 12:00:24 +0200
Subject: [PATCH 1/4] avcodec/mpegaudiodec_template: Don't modify
 AVCodecContext.priv_data

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/mpegaudiodec_template.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/libavcodec/mpegaudiodec_template.c b/libavcodec/mpegaudiodec_template.c
index d7c5210eb8..5c38f4e9d7 100644
--- a/libavcodec/mpegaudiodec_template.c
+++ b/libavcodec/mpegaudiodec_template.c
@@ -280,10 +280,9 @@ static av_cold void decode_init_static(void)
     ff_mpegaudiodec_common_init_static();
 }
 
-static av_cold int decode_init(AVCodecContext * avctx)
+static av_cold int decode_ctx_init(AVCodecContext *avctx, MPADecodeContext *s)
 {
     static AVOnce init_static_once = AV_ONCE_INIT;
-    MPADecodeContext *s = avctx->priv_data;
 
     s->avctx = avctx;
 
@@ -315,6 +314,11 @@ static av_cold int decode_init(AVCodecContext * avctx)
     return 0;
 }
 
+static av_cold int decode_init(AVCodecContext *avctx)
+{
+    return decode_ctx_init(avctx, avctx->priv_data);
+}
+
 #define C3 FIXHR(0.86602540378443864676/2)
 #define C4 FIXHR(0.70710678118654752439/2) //0.5 / cos(pi*(9)/36)
 #define C5 FIXHR(0.51763809020504152469/2) //0.5 / cos(pi*(5)/36)
@@ -1771,19 +1775,13 @@ static av_cold int decode_init_mp3on4(AVCodecContext * avctx)
         s->syncword = 0xfff00000;
 
     /* Init the first mp3 decoder in standard way, so that all tables get built
-     * We replace avctx->priv_data with the context of the first decoder so that
-     * decode_init() does not have to be changed.
      * Other decoders will be initialized here copying data from the first context
      */
     // Allocate zeroed memory for the first decoder context
     s->mp3decctx[0] = av_mallocz(sizeof(MPADecodeContext));
     if (!s->mp3decctx[0])
         return AVERROR(ENOMEM);
-    // Put decoder context in place to make init_decode() happy
-    avctx->priv_data = s->mp3decctx[0];
-    ret = decode_init(avctx);
-    // Restore mp3on4 context pointer
-    avctx->priv_data = s;
+    ret = decode_ctx_init(avctx, s->mp3decctx[0]);
     if (ret < 0)
         return ret;
     s->mp3decctx[0]->adu_mode = 1; // Set adu mode
-- 
2.49.1


>From fb818736d4a9ef8eafd85c97c0f2ff2c31ff6703 Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Thu, 4 Sep 2025 12:07:06 +0200
Subject: [PATCH 2/4] avcodec/mpegaudiodec_template: Allocate sub-contexts
 jointly

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/mpegaudiodec_template.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/libavcodec/mpegaudiodec_template.c b/libavcodec/mpegaudiodec_template.c
index 5c38f4e9d7..42e995643b 100644
--- a/libavcodec/mpegaudiodec_template.c
+++ b/libavcodec/mpegaudiodec_template.c
@@ -1738,10 +1738,8 @@ static const int16_t chan_layout[8] = {
 static av_cold int decode_close_mp3on4(AVCodecContext * avctx)
 {
     MP3On4DecodeContext *s = avctx->priv_data;
-    int i;
 
-    for (i = 0; i < s->frames; i++)
-        av_freep(&s->mp3decctx[i]);
+    av_freep(&s->mp3decctx[0]);
 
     return 0;
 }
@@ -1777,8 +1775,8 @@ static av_cold int decode_init_mp3on4(AVCodecContext * avctx)
     /* Init the first mp3 decoder in standard way, so that all tables get built
      * Other decoders will be initialized here copying data from the first context
      */
-    // Allocate zeroed memory for the first decoder context
-    s->mp3decctx[0] = av_mallocz(sizeof(MPADecodeContext));
+    // Allocate zeroed memory for the decoder contexts
+    s->mp3decctx[0] = av_calloc(s->frames, sizeof(*s->mp3decctx[0]));
     if (!s->mp3decctx[0])
         return AVERROR(ENOMEM);
     ret = decode_ctx_init(avctx, s->mp3decctx[0]);
@@ -1790,9 +1788,7 @@ static av_cold int decode_init_mp3on4(AVCodecContext * avctx)
      * Each frame is 1 or 2 channels - up to 5 frames allowed
      */
     for (i = 1; i < s->frames; i++) {
-        s->mp3decctx[i] = av_mallocz(sizeof(MPADecodeContext));
-        if (!s->mp3decctx[i])
-            return AVERROR(ENOMEM);
+        s->mp3decctx[i] = s->mp3decctx[0] + i;
         s->mp3decctx[i]->adu_mode = 1;
         s->mp3decctx[i]->avctx = avctx;
         s->mp3decctx[i]->mpadsp = s->mp3decctx[0]->mpadsp;
-- 
2.49.1


>From 3e1a4eb308100f30b7b141ec5390f1ff7121ef77 Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Thu, 4 Sep 2025 12:25:48 +0200
Subject: [PATCH 3/4] avcodec/mpegaudiodec_template: Mark flush functions as
 av_cold

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/mpegaudiodec_template.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libavcodec/mpegaudiodec_template.c b/libavcodec/mpegaudiodec_template.c
index 42e995643b..3ca9adb8ab 100644
--- a/libavcodec/mpegaudiodec_template.c
+++ b/libavcodec/mpegaudiodec_template.c
@@ -1625,7 +1625,7 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
     return buf_size + skipped;
 }
 
-static void mp_flush(MPADecodeContext *ctx)
+static av_cold void mp_flush(MPADecodeContext *ctx)
 {
     memset(ctx->synth_buf, 0, sizeof(ctx->synth_buf));
     memset(ctx->mdct_buf, 0, sizeof(ctx->mdct_buf));
@@ -1633,7 +1633,7 @@ static void mp_flush(MPADecodeContext *ctx)
     ctx->dither_state = 0;
 }
 
-static void flush(AVCodecContext *avctx)
+static av_cold void flush(AVCodecContext *avctx)
 {
     mp_flush(avctx->priv_data);
 }
@@ -1799,7 +1799,7 @@ static av_cold int decode_init_mp3on4(AVCodecContext * avctx)
 }
 
 
-static void flush_mp3on4(AVCodecContext *avctx)
+static av_cold void flush_mp3on4(AVCodecContext *avctx)
 {
     int i;
     MP3On4DecodeContext *s = avctx->priv_data;
-- 
2.49.1


>From 407c8ae0e89573da2aad0845bb1f58ba760b2b3d Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Thu, 4 Sep 2025 12:29:28 +0200
Subject: [PATCH 4/4] avcodec/mpegaudiodec_template: Avoid write-only stores

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/mpegaudiodec_template.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libavcodec/mpegaudiodec_template.c b/libavcodec/mpegaudiodec_template.c
index 3ca9adb8ab..0efcf9853d 100644
--- a/libavcodec/mpegaudiodec_template.c
+++ b/libavcodec/mpegaudiodec_template.c
@@ -1792,7 +1792,9 @@ static av_cold int decode_init_mp3on4(AVCodecContext * avctx)
         s->mp3decctx[i]->adu_mode = 1;
         s->mp3decctx[i]->avctx = avctx;
         s->mp3decctx[i]->mpadsp = s->mp3decctx[0]->mpadsp;
+#if USE_FLOATS
         s->mp3decctx[i]->butterflies_float = s->mp3decctx[0]->butterflies_float;
+#endif
     }
 
     return 0;
-- 
2.49.1

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