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avcodec/adpcm_ima_amv: document header format

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Signed-off-by: Zane van Iperen <zane@zanevaniperen.com>
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Zane van Iperen 2020-11-02 15:47:26 +10:00
parent 50d3a751aa
commit 8903cb3c15
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1 changed files with 10 additions and 0 deletions
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libavcodec/adpcm.c
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@ -1690,6 +1690,16 @@ static int adpcm_decode_frame(AVCodecContext *avctx, void *data,
case AV_CODEC_ID_ADPCM_IMA_AMV: case AV_CODEC_ID_ADPCM_IMA_AMV:
av_assert0(avctx->channels == 1); av_assert0(avctx->channels == 1);
/*
* Header format:
* int16_t predictor;
* uint8_t step_index;
* uint8_t reserved;
* uint32_t frame_size;
*
* Some implementations have step_index as 16-bits, but others
* only use the lower 8 and store garbage in the upper 8.
*/
c->status[0].predictor = sign_extend(bytestream2_get_le16u(&gb), 16); c->status[0].predictor = sign_extend(bytestream2_get_le16u(&gb), 16);
c->status[0].step_index = bytestream2_get_byteu(&gb); c->status[0].step_index = bytestream2_get_byteu(&gb);
bytestream2_skipu(&gb, 5); bytestream2_skipu(&gb, 5);