[FFmpeg-devel] [PATCH 1/2] decode: add ff_decode_skip_samples function

[FFmpeg-devel] [PATCH 1/2] decode: add ff_decode_skip_samples function

[Lynne]

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This is a convenience function, which is required to be called by decoders
needing to skip samples every time.
It automatically creates and increments side data.

This function is a simplified version of an earlier patch. It is only
able to add additional delay, rather than insert or override any.


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From 3045ac286538641076ce4547cda677c3b159877f Mon Sep 17 00:00:00 2001
From: Lynne <dev@lynne.ee>
Date: Mon, 30 Oct 2023 05:38:17 +0100
Subject: [PATCH 1/2] decode: add ff_decode_skip_samples function

This is a convenience function, which is required to be called by decoders
needing to skip samples every time.
It automatically creates and increments side data.

This function is a simplified version of an earlier patch. It is only
able to add additional delay, rather than insert or override any.
---
 libavcodec/decode.c | 17 +++++++++++++++++
 libavcodec/decode.h |  8 ++++++++
 2 files changed, 25 insertions(+)

diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index 2cfb3fcf97..450d63d947 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -299,6 +299,23 @@ static int64_t guess_correct_pts(AVCodecContext *ctx,
     return pts;
 }
 
+int ff_decode_skip_samples(AVCodecContext *avctx, AVFrame *frame, uint32_t skip)
+{
+    uint32_t val = 0;
+    AVFrameSideData *side = av_frame_get_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES);
+    if (!side) {
+        side = av_frame_new_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES, 10);
+        if (!side)
+            return AVERROR(ENOMEM);
+    }
+
+    val += AV_RL32(side->data);
+    val += skip;
+    AV_WL32(side->data, val);
+
+    return 0;
+}
+
 static int discard_samples(AVCodecContext *avctx, AVFrame *frame, int64_t *discarded_samples)
 {
     AVCodecInternal *avci = avctx->internal;
diff --git a/libavcodec/decode.h b/libavcodec/decode.h
index daf1a67444..c83476208c 100644
--- a/libavcodec/decode.h
+++ b/libavcodec/decode.h
@@ -155,4 +155,12 @@ int ff_hwaccel_frame_priv_alloc(AVCodecContext *avctx, void **hwaccel_picture_pr
 const AVPacketSideData *ff_get_coded_side_data(const AVCodecContext *avctx,
                                                enum AVPacketSideDataType type);
 
+/**
+ * Skip samples in an AVFrame.
+ *
+ * @param skip amount of samples to skip unconditionally
+ */
+int ff_decode_skip_samples(AVCodecContext *avctx, AVFrame *frame,
+                           uint32_t skip);
+
 #endif /* AVCODEC_DECODE_H */
-- 
2.43.0


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[FFmpeg-devel] [PATCH 2/2] aacdec: fix single-sample delay for SBR streams

[Lynne]

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Our SBR implementation introduces a single sample of latency into the
output, which is currently never skipped.
This delay is separate from any container skip value and always present,
as it is from an additional part of the decoding process.

Fixes Trac issue #9667


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From 5b9d971b108677d54bc3aac317669007462dbcc9 Mon Sep 17 00:00:00 2001
From: Lynne <dev@lynne.ee>
Date: Mon, 30 Oct 2023 05:40:22 +0100
Subject: [PATCH 2/2] aacdec: fix single-sample delay for SBR streams

Our SBR implementation introduces a single sample of latency into the
output, which is currently never skipped.
This delay is separate from any container skip value and always present,
as it is from an additional part of the decoding process.

Fixes Trac issue #9667
---
 libavcodec/aac.h             |  1 +
 libavcodec/aacdec_template.c | 23 ++++++++++++++++++-----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/libavcodec/aac.h b/libavcodec/aac.h
index 285d3b7482..06ae2222cf 100644
--- a/libavcodec/aac.h
+++ b/libavcodec/aac.h
@@ -298,6 +298,7 @@ struct AACContext {
     AVCodecContext *avctx;
     AVFrame *frame;
 
+    int skip_samples;
     int is_saved;                 ///< Set if elements have stored overlap from previous frame.
     DynamicRangeControl che_drc;
 
diff --git a/libavcodec/aacdec_template.c b/libavcodec/aacdec_template.c
index 2b3509c85f..a82cd69a60 100644
--- a/libavcodec/aacdec_template.c
+++ b/libavcodec/aacdec_template.c
@@ -529,6 +529,8 @@ static void flush(AVCodecContext *avctx)
             }
         }
     }
+
+    ac->skip_samples = 1;
 }
 
 /**
@@ -1222,6 +1224,7 @@ static av_cold int aac_decode_init(AVCodecContext *avctx)
         return AVERROR(ENOMEM);
     }
 
+    ac->skip_samples = 1;
     ac->random_state = 0x1f2e3d4c;
 
 #define MDCT_INIT(s, fn, len, sval)                                            \
@@ -2390,7 +2393,7 @@ static int decode_dynamic_range(DynamicRangeControl *che_drc,
 
 static int decode_fill(AACContext *ac, GetBitContext *gb, int len) {
     uint8_t buf[256];
-    int i, major, minor;
+    int i;
 
     if (len < 13+7*8)
         goto unknown;
@@ -2404,10 +2407,6 @@ static int decode_fill(AACContext *ac, GetBitContext *gb, int len) {
     if (ac->avctx->debug & FF_DEBUG_PICT_INFO)
         av_log(ac->avctx, AV_LOG_DEBUG, "FILL:%s\n", buf);
 
-    if (sscanf(buf, "libfaac %d.%d", &major, &minor) == 2){
-        ac->avctx->internal->skip_samples = 1024;
-    }
-
 unknown:
     skip_bits_long(gb, len);
 
@@ -3374,6 +3373,20 @@ static int aac_decode_frame(AVCodecContext *avctx, AVFrame *frame,
         if (buf[buf_offset])
             break;
 
+    if (ac->skip_samples) {
+        int skip = 0;
+
+        /* Our SBR implementation introduces a sample of delay into the output. */
+        if (ac->oc[1].m4ac.sbr)
+            skip = 1;
+
+        err = ff_decode_skip_samples(avctx, frame, skip);
+        if (err < 0)
+            return err;
+
+        ac->skip_samples = 0;
+    }
+
     return buf_size > buf_offset ? buf_consumed : buf_size;
 }
 
-- 
2.43.0


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Re: [FFmpeg-devel] [PATCH 2/2] aacdec: fix single-sample delay for SBR streams

[Michael Niedermayer]

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On Mon, Dec 04, 2023 at 08:52:06AM +0100, Lynne wrote:
> Our SBR implementation introduces a single sample of latency into the
> output, which is currently never skipped.
> This delay is separate from any container skip value and always present,
> as it is from an additional part of the decoding process.
> 
> Fixes Trac issue #9667
> 

>  aac.h             |    1 +
>  aacdec_template.c |   23 ++++++++++++++++++-----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 100f2e0512732bbf24f36e1524e07fb6c3fa0831  0002-aacdec-fix-single-sample-delay-for-SBR-streams.patch
> From 5b9d971b108677d54bc3aac317669007462dbcc9 Mon Sep 17 00:00:00 2001
> From: Lynne <dev@lynne.ee>
> Date: Mon, 30 Oct 2023 05:40:22 +0100
> Subject: [PATCH 2/2] aacdec: fix single-sample delay for SBR streams
> 
> Our SBR implementation introduces a single sample of latency into the
> output, which is currently never skipped.
> This delay is separate from any container skip value and always present,
> as it is from an additional part of the decoding process.
> 
> Fixes Trac issue #9667
> ---
>  libavcodec/aac.h             |  1 +
>  libavcodec/aacdec_template.c | 23 ++++++++++++++++++-----
>  2 files changed, 19 insertions(+), 5 deletions(-)

this affects many fate tests

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Does the universe only have a finite lifespan? No, its going to go on
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