[PR] avcodec/aacenc: export discard padding side data when needed (PR #23675)

PR #23675 opened by James Almer (jamrial)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23675
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23675.patch

This is in line with other encoders, and is needed by the matroska muxer to properly signal end trimming samples.

fate-gaplessenc-pcm-to-mov-aac changes as the mov muxer now uses this information when writing the edit list, so the shorter frame duration is not needed.


>From 490c9042e45bed3f85099aeece48e6f4f105043c Mon Sep 17 00:00:00 2001
From: James Almer <[email protected]>
Date: Wed, 1 Jul 2026 17:00:42 +0000
Subject: [PATCH] avcodec/aacenc: export discard padding side data when needed

This is in line with other encoders, and is needed by the matroska muxer
to properly signal end trimming samples.

gaplessenc-pcm-to-mov-aac changes as the mov muxer now uses this information
when writing the edit list, so the shorter frame duration is not needed.

Signed-off-by: James Almer <[email protected]>
---
 libavcodec/aacenc.c                      | 9 +++++++++
 tests/ref/fate/gaplessenc-pcm-to-mov-aac | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index d5abb0aa77..a4243350eb 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -1415,6 +1415,15 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
     ff_af_queue_remove(&s->afq, avctx->frame_size, &avpkt->pts,
                        &avpkt->duration);
 
+    int discard_padding = avctx->frame_size - ff_samples_from_time_base(avctx, avpkt->duration);
+    if (discard_padding > 0) {
+        uint8_t *side_data =
+            av_packet_new_side_data(avpkt, AV_PKT_DATA_SKIP_SAMPLES, 10);
+        if (!side_data)
+            return AVERROR(ENOMEM);
+        AV_WL32(side_data + 4, discard_padding);
+    }
+
     avpkt->flags |= AV_PKT_FLAG_KEY;
 
     *got_packet_ptr = 1;
diff --git a/tests/ref/fate/gaplessenc-pcm-to-mov-aac b/tests/ref/fate/gaplessenc-pcm-to-mov-aac
index 073f2ec0c1..2c2429e661 100644
--- a/tests/ref/fate/gaplessenc-pcm-to-mov-aac
+++ b/tests/ref/fate/gaplessenc-pcm-to-mov-aac
@@ -22,7 +22,7 @@ packet|pts=524288|dts=524288|duration=1024|flags=K__
 packet|pts=525312|dts=525312|duration=1024|flags=K__
 packet|pts=526336|dts=526336|duration=1024|flags=K__
 packet|pts=527360|dts=527360|duration=1024|flags=K__
-packet|pts=528384|dts=528384|duration=816|flags=K__|side_datum/skip_samples:side_data_type=Skip Samples|side_datum/skip_samples:skip_samples=0|side_datum/skip_samples:discard_padding=208|side_datum/skip_samples:skip_reason=0|side_datum/skip_samples:discard_reason=0
+packet|pts=528384|dts=528384|duration=1024|flags=K__|side_datum/skip_samples:side_data_type=Skip Samples|side_datum/skip_samples:skip_samples=0|side_datum/skip_samples:discard_padding=208|side_datum/skip_samples:skip_reason=0|side_datum/skip_samples:discard_reason=0
 stream|nb_read_packets=518
 frame|pts=0|pkt_dts=0|best_effort_timestamp=0|nb_samples=1024
 frame|pts=1024|pkt_dts=1024|best_effort_timestamp=1024|nb_samples=1024
-- 
2.52.0

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