ffmpeg: Correct inter stream timestamp discontinuities

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

ffmpeg.h

@@ -278,6 +278,7 @@ typedef struct InputFile {
     int eagain;           /* true if last read attempt returned EAGAIN */
     int ist_index;        /* index of first stream in input_streams */
     int64_t ts_offset;
+    int64_t last_ts;
     int nb_streams;       /* number of stream that ffmpeg is aware of; may be different
                              from ctx.nb_streams if new streams appear during av_read_frame() */
     int nb_streams_warn;  /* number of streams that the user was warned of */