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avcodec/adpcm: Fix step_index decoding by skipping padding byte

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The bug was caused by incorrect reading of the step_index field: the original
code read a 16-bit value (including a padding byte) instead of the correct
8-bit step_index as defined by the ADPCM format. This led to distorted audio
or incorrect step calculations when decoding specific ADPCM-encoded files.

Fix by:
1. Reading step_index as an 8-bit unsigned byte via bytestream2_get_byteu()
2. Skipping the subsequent 8-bit padding byte with bytestream2_skip()
This commit is contained in:
tangsha
2025-12-01 16:15:35 +08:00
committed by Marton Balint
parent ecd2919174
commit d28250eada
1 changed files with 2 additions and 1 deletions
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libavcodec/adpcm.c
+2 -1
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@@ -1512,7 +1512,8 @@ static int adpcm_decode_frame(AVCodecContext *avctx, AVFrame *frame,
ADPCMChannelStatus *cs = &c->status[i];
cs->predictor = samples_p[i][0] = sign_extend(bytestream2_get_le16u(&gb), 16);
cs->step_index = sign_extend(bytestream2_get_le16u(&gb), 16);
cs->step_index = bytestream2_get_byteu(&gb);
bytestream2_skipu(&gb, 1);
if (cs->step_index > 88u){
av_log(avctx, AV_LOG_ERROR, "ERROR: step_index[%d] = %i\n",
i, cs->step_index);