From e3c14eaa54c87d4d8771bc75cb24b0b537fbcd19 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Sat, 18 Feb 2017 19:41:02 +0100 Subject: [PATCH] speedhq: fix decoding artifacts The quantization table is stored in the natural order, but when we access it, we use an index that's in zigzag order, causing us to read the wrong value. This causes artifacts, especially in areas with horizontal or vertical edges. The artifacts look a lot like the DCT ringing artifacts you'd expect to see from a low-bitrate file, but when comparing to NewTek's own decoder, it's obvious they're not supposed to be there. Fix by simply storing the scaled quantization table in zigzag order. Performance is unchanged. Reviewed-by: Paul B Mahol Signed-off-by: Michael Niedermayer --- libavcodec/speedhq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libavcodec/speedhq.c b/libavcodec/speedhq.c index 45ee37a4e6..60efb0222b 100644 --- a/libavcodec/speedhq.c +++ b/libavcodec/speedhq.c @@ -409,7 +409,7 @@ static int decode_speedhq_field(const SHQContext *s, const uint8_t *buf, int buf static void compute_quant_matrix(int *output, int qscale) { int i; - for (i = 0; i < 64; i++) output[i] = unscaled_quant_matrix[i] * qscale; + for (i = 0; i < 64; i++) output[i] = unscaled_quant_matrix[ff_zigzag_direct[i]] * qscale; } static int speedhq_decode_frame(AVCodecContext *avctx, -- 2.11.0