The first byte contains compression level together with keyframe status.
When a frame is not interpreted correctly, its data is summed to the
reference, and would degrade over time, producing an incorrect result.

Signed-off-by: Vittorio Giovara <[email protected]>
---
 libavcodec/screenpresso.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/libavcodec/screenpresso.c b/libavcodec/screenpresso.c
index 9635b60..8519a2d 100644
--- a/libavcodec/screenpresso.c
+++ b/libavcodec/screenpresso.c
@@ -115,11 +115,9 @@ static int screenpresso_decode_frame(AVCodecContext 
*avctx, void *data,
         return AVERROR_INVALIDDATA;
     }
 
-    /* Basic sanity check, but not really harmful */
-    if (avpkt->data[0] != 0x72 && avpkt->data[0] != 0x73)
-        av_log(avctx, AV_LOG_WARNING, "Unknown header 0x%02X\n", 
avpkt->data[0]);
-
-    keyframe = (avpkt->data[0] == 0x73);
+    /* Compression level and keyframe information */
+    av_log(avctx, AV_LOG_DEBUG, "Compression level %d\n", avpkt->data[0] >> 4);
+    keyframe = (avpkt->data[0] & 0x03 == 3);
 
     /* Pixel size */
     switch (avpkt->data[1]) {
-- 
2.7.3

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