PR #21548 opened by Lynne URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21548 Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21548.patch
This issue hid under the radar since the codebooks between coupling modes very often result in identical bit counts regardless of the encoded data, leading to no frame-level bitstream desyncs except in rare cases. AAC Mps212 data is parsed immediately after the SBR data, where a loss of sync in SBR will result in Mps212 being wildly different. >From 82b768cfae1a1f69cb5ae927496083b935ce3837 Mon Sep 17 00:00:00 2001 From: Lynne <[email protected]> Date: Thu, 22 Jan 2026 19:58:31 +0100 Subject: [PATCH] aacsbr_template: fix SBR USAC coupling This issue hid under the radar since the codebooks between coupling modes very often result in identical bit counts regardless of the encoded data, leading to no frame-level bitstream desyncs except in rare cases. AAC Mps212 data is parsed immediately after the SBR data, where a loss of sync in SBR will result in Mps212 being wildly different. --- libavcodec/aacsbr_template.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/libavcodec/aacsbr_template.c b/libavcodec/aacsbr_template.c index 3c39da509d..dd9340ff2c 100644 --- a/libavcodec/aacsbr_template.c +++ b/libavcodec/aacsbr_template.c @@ -1287,6 +1287,8 @@ int ff_aac_sbr_decode_usac_data(AACDecContext *ac, ChannelElement *che, if ((sbr->data[0].bs_add_harmonic_flag = get_bits1(gb))) get_bits1_vector(gb, sbr->data[0].bs_add_harmonic, sbr->n[1]); } else if (get_bits1(gb)) { /* bs_coupling == 1 */ + sbr->coupling = 1; + /* if (harmonicSBR) ... */ if (read_sbr_grid(ac, sbr, gb, &sbr->data[0])) @@ -1317,7 +1319,10 @@ int ff_aac_sbr_decode_usac_data(AACDecContext *ac, ChannelElement *che, if ((sbr->data[1].bs_add_harmonic_flag = get_bits1(gb))) get_bits1_vector(gb, sbr->data[1].bs_add_harmonic, sbr->n[1]); } else { /* bs_coupling == 0 */ + sbr->coupling = 0; + /* if (harmonicSBR) ... */ + if (read_sbr_grid(ac, sbr, gb, &sbr->data[0])) return -1; if (read_sbr_grid(ac, sbr, gb, &sbr->data[1])) -- 2.52.0 _______________________________________________ ffmpeg-devel mailing list -- [email protected] To unsubscribe send an email to [email protected]
