avcodec: Fix duration error after seek operation

After seek, s->duration need recalculation, AVCodecParserContext need be set
again. Without the fix, the first audio packet would be dropped after
compute_pkt_fields() as the final pts/dts become invalid.

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

libavcodec/cook_parser.c

@@ -40,11 +40,12 @@ static int cook_parse(AVCodecParserContext *s1, AVCodecContext *avctx,
 {
     CookParseContext *s = s1->priv_data;
 
-    if (s->duration)
-        s1->duration = s->duration;
-    else if (avctx->extradata && avctx->extradata_size >= 8 && avctx->channels)
+    if (!s->duration &&
+                avctx->extradata && avctx->extradata_size >= 8 && avctx->channels)
         s->duration = AV_RB16(avctx->extradata + 4) / avctx->channels;
 
+    s1->duration = s->duration;
+
     /* always return the full packet. this parser isn't doing any splitting or
        combining, only setting packet duration */
     *poutbuf      = buf;