Use av_ts2str() for AVFrame.pkt_dts/pts to avoid print the
pkt_dts/pts as negative number like:
"0,    3616613, -9223372036854775808,     1001,  3110400, 0x75e37a65"
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Jun Zhao <mypopydev@gmail.com>