swr: Use a temporary buffer for dither/Noise shaping when the input is read only

This avoids copying the input

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 2 insertions, 0 deletions

diff --git a/libswresample/dither.c b/libswresample/dither.c
index d7a5b6b558..ae56c8c3ee 100644
--- a/libswresample/dither.c
+++ b/libswresample/dither.c
@@ -115,7 +115,9 @@ int swri_dither_init(SwrContext *s, enum AVSampleFormat out_fmt, enum AVSampleFo
         s->dither.method = SWR_DITHER_TRIANGULAR_HIGHPASS;
     }
 
+    av_assert0(!s->preout.count);
     s->dither.noise = s->preout;
+    s->dither.temp  = s->preout;
     if (s->dither.method > SWR_DITHER_NS) {
         s->dither.noise.bps = 4;
         s->dither.noise.fmt = AV_SAMPLE_FMT_FLTP;